Short note on magnetic impurities in SmFeAsO$_{1-x}$F$_x$ (x=0, 0.07) compounds revealed by

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英美报刊选读(辅修) 磁能

英美报刊选读（辅修）磁能Magnetic Energy: The Future of Power GenerationMagnetic energy, also known as magnetism, is a fundamental force of nature that manifests itself in the interaction between magnetic fields and electric charges. This phenomenon has been known and studied for centuries, but it is only in recent years that researchers have begun to e某plore its potential as a source of energy.At its most basic level, magnetic energy is generated by the movement of electrons within a magnetic field. This movement creates a flow of energy that can be harnessed through the useof magnets and coils of wire. This process is known as electromagnetic induction, and it is the principle behind the operation of generators and motors.The potential of magnetic energy as a source of power lies in its abundance. Magnetic fields are found all around us, from the earth's magnetic field to the magnetic fields generated by permanent magnets. Unlike fossil fuels and other non-renewable sources of energy, magnetic energy is infinitely renewable and sustainable.One of the most promising applications of magnetic energy is in the development of magnetic generators. These devices use magnetic fields to generate electricity without the need forfuel or other e某ternal sources of energy. Magnetic generators are highly efficient and e某tremely reliable, making them an ideal choice for powering homes and businesses.。

中国地质大学(北京)考博专业英复习材料

晶） is said to have a porphyritic texture（斑状结构）. The classification of fine-grained rocks, then, is based on the proportion of minerals which form phenocrysts and these phenocrysts （斑晶）reflect the general composition of the remainder(残留) of the rock. The fine-grained portion of a porphyritic（斑岩） rock is generally referred to as the groundmass（基质） of the phenocrysts. The terms "porphyritic" and "phenocrysts" are not restricted to fine-grained rocks but may also apply to coarse-grained rocks which contain a few crystals distinctly larger than the remainder. The term obsidian(黑曜岩) refers to a glassy rock of rhyolitic（流纹岩） composition. In general, fine-grained rocks consisting of small crystals cannot readily be distinguished from③ glassy rocks in which no crystalline material is present at all. The obsidians, however, are generally easily recognized by their black and highly glossy appearanceass of the same composition as obsidian. Apparently the difference between the modes of formation of obsidian and pumice is that in pumice the entrapped water vapors have been able to escape by a frothing（起泡） process which leaves a network of interconnected pore（气孔） spaces, thus giving the rock a highly porous （多孔的）and open appearance（外观较为松散）. ④ Pegmatite（结晶花岗岩） is a rock which is texturally（构造上地） the exact opposite of obsidian. ⑤ Pegmatites are generally formed as dikes associated with major bodies of granite （花岗岩） . They are characterized by extremely large individual crystals （单个晶体） ; in some pegmatites crystals up to several tens of feet in length（宽达几十英尺）have been identified, but the average size is measured in inches （英寸） . Most mineralogical museums contain a large number of spectacular（壮观的） crystals from pegmatites. Peridotite（橄榄岩） is a rock consisting primarily of olivine, though some varieties contain pyroxene（辉石） in addition. It occurs only as coarse-grained intrusives（侵入）, and no extrusive（喷出的） rocks of equivalent chemical composition have ever been found. Tuff （凝灰岩）is a rock which is igneous in one sense （在某种意义上） and sedimentary in another⑥. A tuff is a rock formed from pyroclastic （火成碎屑的）material which has been blown out of a volcano and accumulated on the ground as individual fragments called ash. Two terms（igneous and sedimentary） are useful to refer solely to the composition of igneous rocks regardless of their textures. The term silicic (硅质的)signifies an abundance of silica-rich（富硅） and light-colored minerals（浅色矿物）, such as quartz, potassium feldspar（钾长石）, and sodic plagioclase （钠长石） . The term basic （基性） signifies （意味着） an abundance of dark colored minerals relatively low in silica and high in calcium, iron, and

How long does it take for the Kondo effect to develop

a r X i v :c o n d -m a t /9903240v 1 [c o n d -m a t .m e s -h a l l ] 15 M a r 1999How long does it take for the Kondo eﬀect to develop?Peter NordlanderDepartment of Physics and Rice Quantum Institute,Rice University,Houston,Texas 77251-1892Michael Pustilnik and Yigal MeirPhysics Department,Ben Gurion University,Beer Sheva,84105,IsraelNed S.WingreenNEC Research Institute,4Independence Way,Princeton,NJ 08540David ngrethDepartment of Physics and Astronomy,Rutgers University,Piscataway,NJ 08854-8019The time-development of the Kondo eﬀect is theoretically investigated by studying a quantum dot suddenly shifted into the Kondo regime by a change of voltage on a nearby ing time-dependent versions of both the Anderson and Kondo Hamiltonians,it is shown that after a time t following the voltage shift,the form of the Kondo resonance matches the time-independent resonance at an eﬀective temperature T eﬀ=T /tanh(πT t/2).Relevance of the buildup of the Kondo resonance to the transport current through a quantum dot is demonstrated.PACS numbers:72.15.Qm,85.30.Vw,73.50.MxThe Kondo eﬀect in quantum dots has been observed in several recent experiments [1].Beyond verifying the-oretical predictions [2,3],these experiments demonstrate that quantum dots can serve as an important new tool to study strongly correlated electron systems.Unlike magnetic impurities in metals,the physical parameters of the quantum dot can be varied continuously,which allows,for example,systematic experimental study of the crossover between the Kondo,the mixed-valence,and the non-Kondo regimes.Moreover,the quantum dot sys-tem opens the possibility of directly observing the time-dependent response of a Kondo system,as there is a well developed technology for applying time-dependent per-turbations to dots [4].Along these lines,several theoret-ical works have addressed the behavior of a Kondo impu-rity subject to ac driving [5].However,a clearer picture of the temporal development of many-body correlations is obtained if the impurity is subject to a sudden shift in energy.Speciﬁcally,by applying a step-like impulse to a nearby gate,the dot can be suddenly shifted into the Kondo regime,and the buildup of the correlated state observed in the transport current.In this Letter,we analyze the behavior of a quan-tum dot following a sudden shift into the Kondo regime.The time-dependent spectral function is evaluated within the non-crossing approximation (NCA)[3,6–8],as is the transport current in response to a pulse train.The latter provides an experimental window on the development of the Kondo resonance.Employing the Kondo Hamilto-nian,we show that a ﬁnite development time t is pertur-batively equivalent to an increase in the eﬀective tem-perature.We treat a quantum dot coupled by tunnel barriers to two leads (inset to Fig.2).Only one spin-degenerate level on the dot is considered,which is a good approximation at low temperatures.A time-dependent voltage V g (t )is applied to a nearby gate,causing a proportionate shift in the energy of the level ǫdot (t ).If the Coulomb inter-action between electrons prevents double occupancy of the dot,the system is described by the U =∞Anderson Hamiltonian for a magnetic impurity,σǫdot (t )n σ+ kσǫkσn kσ+(V k c †kσc σ+H .c .) ,(1)with the constraint that the occupation of the dot cannot exceed one electron.Here c †σcreates an electron of spin σin the quantum dot,with n σthe corresponding number operator;c †kσcreates an electron in the leads,with k rep-resenting all quantum numbers other than spin,including the labels,left and right,for the leads.V k is the tunnel-ing matrix element through the appropriate barrier.The quantum dot is occupied by a single electron provided the level energy ǫdot lies at least a resonance width Γdot [9]below the chemical potential of the leads.At low temper-atures,the resulting free spin on the dot forms a singlet with a spin drawn from the electrons in the leads –this is the Kondo eﬀect.The Kondo temperature,beneath which the strongly correlated state is established,is given by T K ≃D ′exp(−π|ǫdot |/Γdot ),where D ′is a high en-ergy cutoﬀ[10].The signature of this correlated state is a peak at the Fermi energy in the spectral density of the dot electrons.This peak,in turn,dramatically enhances transport through the dot,allowing perfect transmission−6.0−4.0−2.00.0ε0.00.51.01.52.02.5ρd o t (ε,t )−0.10.00.1εt<0t=13.8t=27.6t=82.8t=193t=759FIG.1.Spectral density ρdot (ǫ,t )vs.energy ǫat various times following a step-function change in the level energy ǫdot (t )=−5+3θ(t ).The ordinates for positive times are successively oﬀset by 0.5units.For t <0,ρdot (ǫ,t )is iden-tical to the equilibrium spectral density at ǫdot =−5while for the largest time shown it is indistinguishable on this scale from the equilibrium spectral density at ǫdot =−2.Through-out this work energies are given in units of Γdot ,and times in units of 1/Γdot ,with ¯h =1.Here T =0.0025.at zero temperature [2].We employ the non-crossing approximation (NCA)to analyze the spectral density and transport through the dot in the presence of a time-dependent level energy ǫdot (t ).The NCA is based on an exact transformation of the U =∞Anderson model in Eq.(1)into a slave-boson Hamiltonian [6].The latter is then solved self-consistently to second order in the tunneling matrix el-ements V k .The NCA approximation gives reliable re-sults for temperatures down to T <T K ,and its time-dependent formulation has been discussed at length in previous works [7,8].We deﬁne a time-dependent spec-tral density for the dot electrons as [11]ρdot (ǫ,t )≡Re∞dτ2ψα′,S =ββ′c †βσββ′t t’t t’t=0-t=0+t=0+t=0-FIG.3.Contributions of order J 2to the renormalized con-duction electron scattering vertex,from the Kondo Hamilto-nian in Eq.(3).Solid lines are conduction electron propaga-tors and dashed lines are pseudofermion propagators.Sum-mation over internal spins is implied.pseudofermion number is conserved by H K +λn c ,and wehave n c =0for t <0because of the large pseudofermion energy λ→∞,we obtain an abrupt turn on of the Kondo coupling at t =0and all later expectations are taken in the physical subspace n c =1.The analytical signature of the Kondo eﬀect is the log-arithmic divergence of perturbation theory in the dimen-sionless coupling Jρ,where ρis the density of conduction electron states per spin direction at the Fermi level.In-deed,for T <T K perturbation theory in Jρfails,even for small Jρ.For T >T K ,temperature cuts oﬀthe logarith-mic divergencesand perturbationtheoryis reliable [14].We ﬁnd that a ﬁnite time t following a sudden switching on of the Kondo coupling also results in a convergent per-turbation theory.To demonstrate this,we focus on the simplest quantity that diverges in perturbation theory.Speciﬁcally,we calculate the scattering vertex γpp (t,t ′)to order J 2.Physically,this quantity represents the low-est order change in J due to multiple scattering from the Kondo impurity.Since abruptly turning on the Kondo coupling creates a nonequilibrium state of the system,we use Keldysh Green functions with p =±1for the out-ward/backward branches.In time,the Keldysh contour runs from −∞to ∞(p =+1)and then from ∞to −∞(p =−1).As shown in Fig.(3),there are two contri-butions at order J 2,one with the conduction electron line and the pseudofermion line parallel and one with the lines antiparallel.Evaluating the diagrams in Fig.(3),and keeping only logarithmically divergent contributions in addition to the bare vertex,we ﬁnd γpp ′(t,t ′)=pδpp ′J2G pp 0(t −t ′)sgn (t −t ′).(4)(Note that in this order there is no logarithmic contri-bution that is oﬀ-diagonal in the Keldysh indices.)HereG pp 0(t −t ′)is the bare time-ordered (for p =+1)or anti-time-ordered (for p =−1)Green function for conduc-tion electrons at the site of the Kondo impurity.For|t −t ′|≫1/D (D is a high-energy cutoﬀ)it takes the form [15]G pp 0(t −t ′)→−πρT2ρJ lnD2.(6)For T t ≫1this reduces to the usual equilibrium form,γ∝J 1+1T ,with the logarithmic divergence cut oﬀonly by temperature.However,since in our case the Kondo coupling exists only for times t >0,the re-sult contains an additional cutoﬀdue to the ﬁnite time allowed for spin-ﬂip scattering.Formally,the ﬁnite time t since the onset of the Kondo coupling can be absorbed into an increase in the eﬀective temperature,T eﬀ=T¯h Γdot ∂ǫ,(8)where f (ǫ)is the Fermi function,and ¯h is explicitly in-cluded for clarity.If a periodic gate voltage is applied tothe dot,formula (8)is still valid if G is replaced by the time-averaged conductance G ,and ρdot (ǫ)is replaced by the average of the time-dependent spectral density ρdot (ǫ,t ) .Consider a periodic signal consisting of an “on”pulse of duration τon which brings the dot into the Kondo regime followed by an “oﬀ”pulse which moves it back out of the Kondo regime.During each on pulse,ρdot (ǫF ,t )will build up to a maximum at time τon and then rapidly decrease back to a low value during the oﬀpulse.The diﬀerential increase of conductance as the duration of the on100200300400τon [1/Γdot ]0.00.51.01.5d G i n t /d τo n [e 2/h ]T=0.04T=0.02T=0.01T=0.005T=0.0025ττon V (t)goffFIG.4.Solid curves:derivative of G int (in units of e 2/h )with respect to duration τon of “on”gate-voltage pulses,at various temperatures.G int is the conductance inte-grated over a full cycle of gate voltage.Dashed curve:−π dǫΓdot f ′(ǫ)ρdot (ǫ,t =τon )for T =0.0025.Inset:schematic periodic gate-voltage pulse train.The level energy is ǫdot =−2in the on state and ǫdot =−5in the oﬀstate.The duration of the oﬀperiod,τoﬀis long enough to allow transients from each on pulse to die out.pulse is increased will therefore reﬂect the magnitude of the spectral density near or at the Fermi energy at a timeτon following the shift into the Kondo regime.In Fig.(4),we have plotted the diﬀerential with respect to τon of the conductance,with a ﬁxed oﬀ-pulse duration τoﬀ.The conductance is integrated over the period,rather than time-averaged,to remove eﬀects due to the changing du-ration of the period,i.e.G int =(τon +τoﬀ) G .This measurable transport quantity provides a probe of the time-development of the Kondo resonance [18].In conclusion,we have analyzed the response of a quan-tum dot to a sudden shift of gate voltage which takes the dot into the regime of the Kondo eﬀect.The buildup of many-body correlations between the dot and the leads follows an uncertainty principle:at time t the Kondo res-onance is cut oﬀby an energy ∼1/t .Within perturba-tion theory in the Kondo coupling,we ﬁnd that the ﬁnite time t plays the role of an increased eﬀective tempera-ture T eﬀ=T/tanh(πT t/2).To experimentally probe the buildup of the Kondo resonance,we propose applying a train of square gate-voltage pulses to the dot.The deriva-tive of current with respect to duration of the “on”pulse accurately reproduces the time-dependent amplitude of the Kondo resonance.The work was supported in part by NSF grants DMR 95-21444(Rice)and DMR 97-08499(Rutgers).Work at BGU was supported by the The Israel Science Founda-tion -Centers of Excellence Program.One of us (MP)acknowledges the support of a Kreitman Fellowship.D Γdot /4,where 2D is the eﬀectivebandwidth.The calculations here used a parabolic band of total width 40Γdot .[11]A.-P.Jauho,N.S.Wingreen,and Y.Meir,Phys.Rev.B 50,5528(1994).[12]Our calculations are based on the approximation that the switching time,τs ,is exactly zero.In reality,τs is always a ﬁnite time.Our results are valid for ﬁnite τs as well,provided that t ≫τs .[13]J.R.Schrieﬀer and P.A.Wolﬀ,Phys.Rev.149,491(1966).[14]A.A.Abrikosov,Physics 2,5(1965).[15]G.Yuval,and P.W.Anderson,Phys.Rev.B 1,1522(1970).[16]By evaluating the conduction electron self-energy to or-der J 3,we have directly conﬁrmed the ∼1/t cutoﬀfor the Kondo peak in the spectral density.[17]Y.Meir and N.S.Wingreen,Phys.Rev.Lett.68,2512(1992).[18]The diﬀerence between the dashed and solid curves at small τon reﬂects the ﬁnite decay -time of the Kondo res-onance after the pulse is switched oﬀ.。

中英文核磁说明书

中英文核磁说明书Nuclear Magnetic Resonance (NMR) Instructions核磁共振（NMR）说明书1. Introduction: The nuclear magnetic resonance (NMR) technique is widely used in chemistry, physics, and biology for studying the structure, dynamics, and interactions of molecules. This instruction manual provides essential information on how to properly operate an NMR instrument.1. 简介：核磁共振（NMR）技术广泛应用于化学、物理和生物学等领域，用于研究分子的结构、动力学和相互作用。

本说明书提供了正确操作核磁共振仪器的基本信息。

2. Safety precautions: It is crucial to follow safety precautions while working with NMR instruments. This includes wearing appropriate personal protective equipment, ensuring proper ventilation, and maintaining a safe working environment.2. 安全注意事项：使用核磁共振仪器时，必须遵循安全注意事项。

包括穿戴适当的个人防护装备，确保良好通风和维持安全工作环境。

3. Instrument setup: Proper instrument setup is important for obtaining accurate NMR data. This includes calibrating the instrument, optimizing the magnetic field, and ensuring that all necessary components are properly connected.3. 仪器设置：正确的仪器设置对于获取准确的核磁共振数据至关重要。

地球磁场在减弱的证据

地球磁场在减弱的证据英文回答：Evidence of Earth's Weakening Magnetic Field.The Earth's magnetic field, also known as the geomagnetic field, is generated by the movement of molten iron in the outer core of the planet. This magnetic field is crucial for protecting the Earth from harmful solar radiation and maintaining a stable climate. However, there is mounting evidence that the Earth's magnetic field is weakening.One piece of evidence is the observation of the South Atlantic Anomaly (SAA). The SAA is an area in the South Atlantic Ocean where the Earth's magnetic field is significantly weaker than in other regions. Satellites passing through this anomaly experience higher levels of radiation, which can affect their electronic systems. This anomaly has been expanding over the past few decades,indicating a weakening of the Earth's magnetic field.Another piece of evidence comes from studies of ancient rocks. Rocks contain tiny magnetic minerals that align with the Earth's magnetic field at the time of their formation. By analyzing these rocks, scientists can determine the strength and direction of the Earth's magnetic field in the past. These studies have revealed that the Earth's magnetic field has been weakening over the past few centuries.Furthermore, researchers have found that the rate of decline in the Earth's magnetic field has been accelerating in recent years. This rapid decline suggests that the weakening of the magnetic field is not a gradual process but rather a more significant and concerning phenomenon. If this trend continues, it could have significantimplications for our planet.The weakening of Earth's magnetic field has several potential consequences. One of the most significant is the increased exposure to solar radiation. The magnetic field acts as a shield, deflecting charged particles from the Sunaway from the Earth. Without a strong magnetic field, more solar radiation would reach the Earth's surface, increasing the risk of skin cancer and other health issues.Additionally, a weakened magnetic field could have implications for navigation systems that rely on magnetic compasses. The accuracy of compasses could be compromised, leading to errors in navigation. This could be particularly problematic for ships and aircraft that heavily rely on magnetic compasses for direction.In conclusion, there is compelling evidence that the Earth's magnetic field is weakening. The South Atlantic Anomaly, studies of ancient rocks, and the accelerating rate of decline all point to this concerning phenomenon. The implications of a weakened magnetic field range from increased exposure to solar radiation to potential navigation issues. It is crucial for scientists to continue monitoring and studying this phenomenon to better understand its implications for our planet.中文回答：地球磁场减弱的证据。

近藤效应

Tunable Kondo eﬀect in a single donor atomnsbergen 1,G.C.Tettamanzi 1,J.Verduijn 1,N.Collaert 2,S.Biesemans 2,M.Blaauboer 1,and S.Rogge 11Kavli Institute of Nanoscience,Delft University of Technology,Lorentzweg 1,2628CJ Delft,The Netherlands and2InterUniversity Microelectronics Center (IMEC),Kapeldreef 75,3001Leuven,Belgium(Dated:September 30,2009)The Kondo eﬀect has been observed in a single gate-tunable atom.The measurement device consists of a single As dopant incorporated in a Silicon nanostructure.The atomic orbitals of the dopant are tunable by the gate electric ﬁeld.When they are tuned such that the ground state of the atomic system becomes a (nearly)degenerate superposition of two of the Silicon valleys,an exotic and hitherto unobserved valley Kondo eﬀect appears.Together with the “regular”spin Kondo,the tunable valley Kondo eﬀect allows for reversible electrical control over the symmetry of the Kondo ground state from an SU(2)-to an SU(4)-conﬁguration.The addition of magnetic impurities to a metal leads to an anomalous increase of their resistance at low tem-perature.Although discovered in the 1930’s,it took until the 1960’s before this observation was satisfactorily ex-plained in the context of exchange interaction between the localized spin of the magnetic impurity and the de-localized conduction electrons in the metal [1].This so-called Kondo eﬀect is now one of the most widely stud-ied phenomena in condensed-matter physics [2]and plays a mayor role in the ﬁeld of nanotechnology.Kondo ef-fects on single atoms have ﬁrst been observed by STM-spectroscopy and were later discovered in a variety of mesoscopic devices ranging from quantum dots and car-bon nanotubes to single molecules [3].Kondo eﬀects,however,do not only arise from local-ized spins:in principle,the role of the electron spin can be replaced by another degree of freedom,for example or-bital momentum [4].The simultaneous presence of both a spin-and an orbital degeneracy gives rise to an exotic SU(4)-Kondo eﬀect,where ”SU(4)”refers to the sym-metry of the corresponding Kondo ground state [5,6].SU(4)Kondo eﬀects have received quite a lot of theoret-ical attention [6,7],but so far little experimental work exists [8].The atomic orbitals of a gated donor in Si consist of linear combinations of the sixfold degenerate valleys of the Si conduction band.The orbital-(or more speciﬁ-cally valley)-degeneracy of the atomic ground state is tunable by the gate electric ﬁeld.The valley splitting ranges from ∼1meV at high ﬁelds (where the electron is pulled towards the gate interface)to being equal to the donors valley-orbit splitting (∼10-20meV)at low ﬁelds [9,10].This tunability essentially originates from a gate-induced quantum conﬁnement transition [10],namely from Coulombic conﬁnement at the donor site to 2D-conﬁnement at the gate interface.In this article we study Kondo eﬀects on a novel exper-imental system,a single donor atom in a Silicon nano-MOSFET.The charge state of this single dopant can be tuned by the gate electrode such that a single electron (spin)is localized on the pared to quantum dots (or artiﬁcial atoms)in Silicon [11,12,13],gated dopants have a large charging energy compared to the level spac-ing due to their typically much smaller size.As a result,the orbital degree of freedom of the atom starts to play an important role in the Kondo interaction.As we will argue in this article,at high gate ﬁeld,where a (near)de-generacy is created,the valley index forms a good quan-tum number and Valley Kondo [14]eﬀects,which have not been observed before,appear.Moreover,the Valley Kondo resonance in a gated donor can be switched on and oﬀby the gate electrode,which provides for an electri-cally controllable quantum phase transition [15]between the regular SU(2)spin-and the SU(4)-Kondo ground states.In our experiment we use wrap-around gate (FinFET)devices,see Fig.1(a),with a single Arsenic donor in the channel dominating the sub-threshold transport charac-teristics [16].Several recent experiments have shown that the ﬁngerprint of a single dopant can be identiﬁed in low-temperature transport through small CMOS devices [16,17,18].We perform transport spectroscopy (at 4K)on a large ensemble of FinFET devices and select the few that show this ﬁngerprint,which essentially consists of a pair of characteristic transport resonances associ-ated with the one-electron (D 0)-and two-electron (D −)-charge states of the single donor [16].From previous research we know that the valley splitting in our Fin-FET devices is typically on the order of a few meV’s.In this Report,we present several such devices that are in addition characterized by strong tunnel coupling to the source/drain contacts which allows for suﬃcient ex-change processes between the metallic contacts and the atom to observe Kondo eﬀects.Fig.1b shows a zero bias diﬀerential conductance (dI SD /dV SD )trace at 4.2K as a function of gate volt-age (V G )of one of the strongly coupled FinFETs (J17).At the V G such that a donor level in the barrier is aligned with the Fermi energy in the source-drain con-tacts (E F ),electrons can tunnel via the level from source to drain (and vice versa)and we observe an increase in the dI SD /dV SD .The conductance peaks indicated bya r X i v :0909.5602v 1 [c o n d -m a t .m e s -h a l l ] 30 S e p 2009FIG.1:Coulomb blocked transport through a single donor in FinFET devices(a)Colored Scanning Electron Micrograph of a typical FinFET device.(b)Diﬀerential conductance (dI SD/dV SD)versus gate voltage at V SD=0.(D0)and(D−) indicate respectively the transport resonances of the one-and two-electron state of a single As donor located in the Fin-FET channel.Inset:Band diagram of the FinFET along the x-axis,with the(D0)charge state on resonance.(c)and(d) Colormap of the diﬀerential conductance(dI SD/dV SD)as a function of V SD and V G of samples J17and H64.The red dots indicate the(D0)resonances and data were taken at1.6 K.All the features inside the Coulomb diamonds are due to second-order chargeﬂuctuations(see text).(D0)and(D−)are the transport resonances via the one-electron and two-electron charge states respectively.At high gate voltages(V G>450mV),the conduction band in the channel is pushed below E F and the FET channel starts to open.The D−resonance has a peculiar double peak shape which we attribute to capacitive coupling of the D−state to surrounding As atoms[19].The current between the D0and the D−charge state is suppressed by Coulomb blockade.The dI SD/dV SD around the(D0)and(D−)resonances of sample J17and sample H64are depicted in Fig.1c and Fig.1d respectively.The red dots indicate the po-sitions of the(D0)resonance and the solid black lines crossing the red dots mark the outline of its conducting region.Sample J17shows aﬁrst excited state at inside the conducting region(+/-2mV),indicated by a solid black line,associated with the valley splitting(∆=2 mV)of the ground state[10].The black dashed lines indicate V SD=0.Inside the Coulomb diamond there is one electron localized on the single As donor and all the observable transport in this regionﬁnds its origin in second-order exchange processes,i.e.transport via a vir-tual state of the As atom.Sample J17exhibits three clear resonances(indicated by the dashed and dashed-dotted black lines)starting from the(D0)conducting region and running through the Coulomb diamond at-2,0and2mV. The-2mV and2mV resonances are due to a second or-der transition where an electron from the source enters one valley state,an the donor-bound electron leaves from another valley state(see Fig.2(b)).The zero bias reso-nance,however,is typically associated with spin Kondo eﬀects,which happen within the same valley state.In sample H64,the pattern of the resonances looks much more complicated.We observe a resonance around0mV and(interrupted)resonances that shift in V SD as a func-tion of V G,indicating a gradual change of the internal level spectrum as a function of V G.We see a large in-crease in conductance where one of the resonances crosses V SD=0(at V G∼445mV,indicated by the red dashed elipsoid).Here the ground state has a full valley degen-eracy,as we will show in theﬁnal paragraph.There is a similar feature in sample J17at V G∼414mV in Fig.1c (see also the red cross in Fig.1b),although that is prob-ably related to a nearby defect.Because of the relative simplicity of its diﬀerential conductance pattern,we will mainly use data obtained from sample J17.In order to investigate the behavior at the degeneracy point of two valley states we use sample H64.In the following paragraphs we investigate the second-order transport in more detail,in particular its temper-ature dependence,ﬁne-structure,magneticﬁeld depen-dence and dependence on∆.We start by analyzing the temperature(T)dependence of sample J17.Fig.2a shows dI SD/dV SD as a function of V SD inside the Coulomb diamond(at V G=395mV) for a range of temperatures.As can be readily observed from Fig.2a,both the zero bias resonance and the two resonances at V SD=+/-∆mV are suppressed with increasing T.The inset of Fig.2a shows the maxima (dI/dV)MAX of the-2mV and0mV resonances as a function of T.We observe a logarithmic dependence on T(a hallmark sign of Kondo correlations)at both resonances,as indicated by the red line.To investigate this point further we analyze another sample(H67)which has sharper resonances and of which more temperature-dependent data were obtained,see Fig.2c.This sample also exhibits the three resonances,now at∼-1,0and +1mV,and the same strong suppression by tempera-ture.A linear background was removed for clarity.We extracted the(dI/dV)MAX of all three resonances forFIG.2:Electrical transport through a single donor atom in the Coulomb blocked region(a)Diﬀerential conductance of sample J17as a function of V SD in the Kondo regime(at V G=395mV).For clarity,the temperature traces have been oﬀset by50nS with respect to each other.Both the resonances with-and without valley-stateﬂip scale similarly with increasing temperature. Inset:Conductance maxima of the resonances at V SD=-2mV and0mV as a function of temperature.(b)Schematic depiction of three(out of several)second-order processes underlying the zero bias and±∆resonances.(c)Diﬀerential conductance of sample H67as a function of V SD in the Kondo regime between0.3K and6K.A linear(and temperature independent) background on the order of1µS was removed and the traces have been oﬀset by90nS with respect to each other for clarity.(d)The conductance maxima of the three resonances of(c)normalized to their0.3K value.The red line is aﬁt of the data by Eq.1.all temperatures and normalized them to their respective(dI/dV)MAX at300mK.The result is plotted in Fig.2d.We again observe that all three peaks have the same(log-arithmic)dependence on temperature.This dependenceis described well by the following phenomenological rela-tionship[20](dI SD/dV SD)max (T)=(dI SD/dV SD)T 2KT2+TKs+g0(1)where TK =T K/√21/s−1,(dI SD/dV SD)is the zero-temperature conductance,s is a constant equal to0.22 [21]and g0is a constant.Here T K is the Kondo tem-perature.The red curve in Fig.2d is aﬁt of Eq.(1)to the data.We readily observe that the dataﬁt well and extract a T K of2.7K.The temperature scaling demon-strates that both the no valley-stateﬂip resonance at zero bias voltage and the valley-stateﬂip-resonance atﬁnite bias are due to Kondo-type processes.Although a few examples ofﬁnite-bias Kondo have been reported[15,22,23],the corresponding resonances (such as our±∆resonances)are typically associated with in-elastic cotunneling.Aﬁnite bias between the leads breaks the coherence due to dissipative transitions in which electrons are transmitted from the high-potential-lead to the low-potential lead[24].These dissipative4transitions limit the lifetime of the Kondo-type processes and,if strong enough,would only allow for in-elastic events.In the supporting online text we estimate the Kondo lifetime in our system and show it is large enough to sustain theﬁnite-bias Kondo eﬀects.The Kondo nature of the+/-∆mV resonances points strongly towards a Valley Kondo eﬀect[14],where co-herent(second-order)exchange between the delocalized electrons in the contacts and the localized electron on the dopant forms a many-body singlet state that screens the valley index.Together with the more familiar spin Kondo eﬀect,where a many-body state screens the spin index, this leads to an SU(4)-Kondo eﬀect,where the spin and charge degree of freedom are fully entangled[8].The ob-served scaling of the+/-∆-and zero bias-resonances in our samples by a single T K is an indication that such a fourfold degenerate SU(4)-Kondo ground state has been formed.To investigate the Kondo nature of the transport fur-ther,we analyze the substructure of the resonances of sample J17,see Fig.2a.The central resonance and the V SD=-2mV each consist of three separate peaks.A sim-ilar substructure can be observed in sample H67,albeit less clear(see Fig.2c).The substructure can be explained in the context of SU(4)-Kondo in combination with a small diﬀerence between the coupling of the ground state (ΓGS)-and theﬁrst excited state(ΓE1)-to the leads.It has been theoretically predicted that even a small asym-metry(ϕ≡ΓE1/ΓGS∼=1)splits the Valley Kondo den-sity of states into an SU(2)-and an SU(4)-part[25].Thiswill cause both the valley-stateﬂip-and the no valley-stateﬂip resonances to split in three,where the middle peak is the SU(2)-part and the side-peaks are the SU(4)-parts.A more detailed description of the substructure can be found in the supporting online text.The split-ting between middle and side-peaks should be roughly on the order of T K[25].The measured splitting between the SU(2)-and SU(4)-parts equals about0.5meV for sample J17and0.25meV for sample H67,which thus corresponds to T K∼=6K and T K∼=3K respectively,for the latter in line with the Kondo temperature obtained from the temperature dependence.We further note that dI SD/dV SD is smaller than what we would expect for the Kondo conductance at T<T K.However,the only other study of the Kondo eﬀect in Silicon where T K could be determined showed a similar magnitude of the Kondo signal[12].The presence of this substructure in both the valley-stateﬂip-,and the no valley-stateﬂip-Kondo resonance thus also points at a Valley Kondo eﬀect.As a third step,we turn our attention to the magnetic ﬁeld(B)dependence of the resonances.Fig.3shows a colormap plot of dI SD/dV SD for samples J17and H64 both as a function of V SD and B at300mK.The traces were again taken within the Coulomb diamond.Atﬁnite magneticﬁeld,the central Kondo resonances of both de-vices split in two with a splitting of2.2-2.4mV at B=FIG.3:Colormap plot of the conductance as a function of V SD and B of sample J17at V G=395mV(a)and H64at V G=464mV(b).The central Kondo resonances split in two lines which are separated by2g∗µB B.The resonances with a valley-stateﬂip do not seem to split in magneticﬁeld,a feature we associate with the diﬀerent decay-time of parallel and anti-parallel spin-conﬁgurations of the doubly-occupied virtual state(see text).10T.From theoretical considerations we expect the cen-tral Valley Kondo resonance to split in two by∆B= 2g∗µB B if there is no mixing of valley index(this typical 2g∗µB B-splitting of the resonances is one of the hall-marks of the Kondo eﬀect[24]),and to split in three (each separated by g∗µB B)if there is a certain degree of valley index mixing[14].Here,g∗is the g-factor(1.998 for As in Si)andµB is the Bohr magneton.In the case of full mixing of valley index,the valley Kondo eﬀect is expected to vanish and only spin Kondo will remain [25].By comparing our measured magneticﬁeld splitting (∆B)with2g∗µB B,weﬁnd a g-factor between2.1and 2.4for all three devices.This is comparable to the result of Klein et al.who found a g-factor for electrons in SiGe quantum dots in the Kondo regime of around2.2-2.3[13]. The magneticﬁeld dependence of the central resonance5indicates that there is no signiﬁcant mixing of valley in-dex.This is an important observation as the occurrence of Valley Kondo in Si depends on the absence of mix-ing(and thus the valley index being a good quantum number in the process).The conservation of valley in-dex can be attributed to the symmetry of our system. The large2D-conﬁnement provided by the electricﬁeld gives strong reason to believe that the ground-andﬁrst excited-states,E GS and E1,consist of(linear combi-nations of)the k=(0,0,±kz)valleys(with z in the electricﬁeld direction)[10,26].As momentum perpen-dicular to the tunneling direction(k x,see Fig.1)is con-served,also valley index is conserved in tunneling[27]. The k=(0,0,±k z)-nature of E GS and E1should be as-sociated with the absence of signiﬁcant exchange interac-tion between the two states which puts them in the non-interacting limit,and thus not in the correlated Heitler-London limit where singlets and triplets are formed.We further observe that the Valley Kondo resonances with a valley-stateﬂip do not split in magneticﬁeld,see Fig.3.This behavior is seen in both samples,as indicated by the black straight solid lines,and is most easily ob-served in sample J17.These valley-stateﬂip resonances are associated with diﬀerent processes based on their evo-lution with magneticﬁeld.The processes which involve both a valleyﬂip and a spinﬂip are expected to shift to energies±∆±g∗µB B,while those without a spin-ﬂip stay at energies±∆[14,25].We only seem to observe the resonances at±∆,i.e.the valley-stateﬂip resonances without spinﬂip.In Ref[8],the processes with both an orbital and a spinﬂip also could not be observed.The authors attribute this to the broadening of the orbital-ﬂip resonances.Here,we attribute the absence of the processes with spinﬂip to the diﬀerence in life-time be-tween the virtual valley state where two spins in seperate valleys are parallel(τ↑↑)and the virtual state where two spins in seperate valleys are anti-parallel(τ↑↓).In con-trast to the latter,in the parallel spin conﬁguration the electron occupying the valley state with energy E1,can-not decay to the other valley state at E GS due to Pauli spin blockade.It wouldﬁrst needs toﬂip its spin[28].We have estimatedτ↑↑andτ↑↓in our system(see supporting online text)andﬁnd thatτ↑↑>>h/k b T K>τ↑↓,where h/k b T K is the characteristic time-scale of the Kondo pro-cesses.Thus,the antiparallel spin conﬁguration will have relaxed before it has a change to build up a Kondo res-onance.Based on these lifetimes,we do not expect to observe the Kondo resonances associated with both an valley-state-and a spin-ﬂip.Finally,we investigate the degeneracy point of valley states in the Coulomb diamond of sample H64.This degeneracy point is indicated in Fig.1d by the red dashed ellipsoid.By means of the gate electrode,we can tune our system onto-or oﬀthis degeneracy point.The gate-tunability in this sample is created by a reconﬁguration of the level spectrum between the D0and D−-charge states,FIG.4:Colormap plot of I SD at V SD=0as a function of V G and B.For increasing B,a conductance peak develops around V G∼450mV at the valley degeneracy point(∆= 0),indicated by the dashed black line.Inset:Magneticﬁeld dependence of the valley degeneracy point.The resonance is ﬁxed at zero bias and its magnitude does not depend on the magneticﬁeld.probably due to Coulomb interactions in the D−-states. Figure4shows a colormap plot of I SD at V SD=0as a function of V G and B(at0.3K).Note that we are thus looking at the current associated with the central Kondo resonance.At B=0,we observe an increasing I SD for higher V G as the atom’s D−-level is pushed toward E F. As B is increased,the central Kondo resonance splits and moves away from V SD=0,see Fig.3.This leads to a general decrease in I SD.However,at around V G= 450mV a peak in I SD develops,indicated by the dashed black line.The applied B-ﬁeld splits oﬀthe resonances with spin-ﬂip,but it is the valley Kondo resonance here that stays at zero bias voltage giving rise to the local current peak.The inset of Fig.4shows the single Kondo resonance in dI SD/dV SD as a function of V SD and B.We observe that the magnitude of the resonance does not decrease signiﬁcantly with magneticﬁeld in contrast to the situation at∆=0(Fig.3b).This insensitivity of the Kondo eﬀect to magneticﬁeld which occurs only at∆= 0indicates the profound role of valley Kondo processes in our structure.It is noteworthy to mention that at this speciﬁc combination of V SD and V G the device can potentially work as a spin-ﬁlter[6].We acknowledge fruitful discussions with Yu.V. Nazarov,R.Joynt and S.Shiau.This project is sup-ported by the Dutch Foundation for Fundamental Re-search on Matter(FOM).6[1]Kondo,J.,Resistance Minimum in Dilute Magnetic Al-loys,Prog.Theor.Phys.3237-49(1964)[2]Hewson,A.C.,The Kondo Problem to Heavy Fermions(Cambridge Univ.Press,Cambridge,1993).[3]Wingreen N.S.,The Kondo eﬀect in novel systems,Mat.Science Eng.B842225(2001)and references therein.[4]Cox,D.L.,Zawadowski,A.,Exotic Kondo eﬀects in met-als:magnetic ions in a crystalline electricﬁeld and tun-neling centers,Adv.Phys.47,599-942(1998)[5]Inoshita,T.,Shimizu, A.,Kuramoto,Y.,Sakaki,H.,Correlated electron transport through a quantum dot: the multiple-level eﬀect.Phys.Rev.B48,14725-14728 (1993)[6]Borda,L.Zar´a nd,G.,Hofstetter,W.,Halperin,B.I.andvon Delft,J.,SU(4)Fermi Liquid State and Spin Filter-ing in a Double Quantum Dot System,Phys.Rev.Lett.90,026602(2003)[7]Zar´a nd,G.,Orbitalﬂuctuations and strong correlationsin quantum dots,Philosophical Magazine,86,2043-2072 (2006)[8]Jarillo-Herrero,P.,Kong,J.,van der Zant H.S.J.,Dekker,C.,Kouwenhoven,L.P.,De Franceschi,S.,Or-bital Kondo eﬀect in carbon nanotubes,Nature434,484 (2005)[9]Martins,A.S.,Capaz,R.B.and Koiller,B.,Electric-ﬁeldcontrol and adiabatic evolution of shallow donor impuri-ties in silicon,Phys.Rev.B69,085320(2004)[10]Lansbergen,G.P.et al.,Gate induced quantum conﬁne-ment transition of a single dopant atom in a Si FinFET, Nature Physics4,656(2008)[11]Rokhinson,L.P.,Guo,L.J.,Chou,S.Y.,Tsui, D.C.,Kondo-like zero-bias anomaly in electronic transport through an ultrasmall Si quantum dot,Phys.Rev.B60, R16319-R16321(1999)[12]Specht,M.,Sanquer,M.,Deleonibus,S.,Gullegan G.,Signature of Kondo eﬀect in silicon quantum dots,Eur.Phys.J.B26,503-508(2002)[13]Klein,L.J.,Savage, D.E.,Eriksson,M.A.,Coulombblockade and Kondo eﬀect in a few-electron silicon/silicon-germanium quantum dot,Appl.Phys.Lett.90,033103(2007)[14]Shiau,S.,Chutia,S.and Joynt,R.,Valley Kondo eﬀectin silicon quantum dots,Phys.Rev.B75,195345(2007) [15]Roch,N.,Florens,S.,Bouchiat,V.,Wernsdirfer,W.,Balestro, F.,Quantum phase transistion in a single molecule quantum dot,Nature453,633(2008)[16]Sellier,H.et al.,Transport Spectroscopy of a SingleDopant in a Gated Silicon Nanowire,Phys.Rev.Lett.97,206805(2006)[17]Calvet,L.E.,Wheeler,R.G.and Reed,M.A.,Observa-tion of the Linear Stark Eﬀect in a Single Acceptor in Si, Phys.Rev.Lett.98,096805(2007)[18]Hofheinz,M.et al.,Individual charge traps in siliconnanowires,Eur.Phys.J.B54,299307(2006)[19]Pierre,M.,Hofheinz,M.,Jehl,X.,Sanquer,M.,Molas,G.,Vinet,M.,Deleonibus S.,Oﬀset charges acting as ex-cited states in quantum dots spectroscopy,Eur.Phys.J.B70,475-481(2009)[20]Goldhaber-Gordon,D.,Gres,J.,Kastner,M.A.,Shtrik-man,H.,Mahalu, D.,Meirav,U.,From the Kondo Regime to the Mixed-Valence Regime in a Single-Electron Transistor,Phys.Rev.Lett.81,5225(1998) [21]Although the value of s=0.22stems from SU(2)spinKondo processes,it is valid for SU(4)-Kondo systems as well[8,25].[22]Paaske,J.,Rosch,A.,W¨o lﬂe,P.,Mason,N.,Marcus,C.M.,Nyg˙ard,Non-equilibrium singlet-triplet Kondo ef-fect in carbon nanotubes,Nature Physics2,460(2006) [23]Osorio, E.A.et al.,Electronic Excitations of a SingleMolecule Contacted in a Three-Terminal Conﬁguration, Nanoletters7,3336-3342(2007)[24]Meir,Y.,Wingreen,N.S.,Lee,P.A.,Low-TemperatureTransport Through a Quantum Dot:The Anderson Model Out of Equilibrium,Phys.Rev.Lett.70,2601 (1993)[25]Lim,J.S.,Choi,M-S,Choi,M.Y.,L´o pez,R.,Aguado,R.,Kondo eﬀects in carbon nanotubes:From SU(4)to SU(2)symmetry,Phys.Rev.B74,205119(2006) [26]Hada,Y.,Eto,M.,Electronic states in silicon quan-tum dots:Multivalley artiﬁcial atoms,Phys.Rev.B68, 155322(2003)[27]Eto,M.,Hada,Y.,Kondo Eﬀect in Silicon QuantumDots with Valley Degeneracy,AIP Conf.Proc.850,1382-1383(2006)[28]A comparable process in the direct transport throughSi/SiGe double dots(Lifetime Enhanced Transport)has been recently proposed[29].[29]Shaji,N.et.al.,Spin blockade and lifetime-enhancedtransport in a few-electron Si/SiGe double quantum dot, Nature Physics4,540(2008)7Supporting InformationFinFET DevicesThe FinFETs used in this study consist of a silicon nanowire connected to large contacts etched in a60nm layer of p-type Silicon On Insulator.The wire is covered with a nitrided oxide(1.4nm equivalent SiO2thickness) and a narrow poly-crystalline silicon wire is deposited perpendicularly on top to form a gate on three faces.Ion implantation over the entire surface forms n-type degen-erate source,drain,and gate electrodes while the channel protected by the gate remains p-type,see Fig.1a of the main article.The conventional operation of this n-p-n ﬁeld eﬀect transistor is to apply a positive gate voltage to create an inversion in the channel and allow a current toﬂow.Unintentionally,there are As donors present be-low the Si/SiO2interface that show up in the transport characteristics[1].Relation between∆and T KThe information obtained on T K in the main article allows us to investigate the relation between the splitting (∆)of the ground(E GS)-andﬁrst excited(E1)-state and T K.It is expected that T K decreases as∆increases, since a high∆freezes out valley-stateﬂuctuations.The relationship between T K of an SU(4)system and∆was calculated by Eto[2]in a poor mans scaling approach ask B T K(∆) B K =k B T K(∆=0)ϕ(2)whereϕ=ΓE1/ΓGS,withΓE1andΓGS the lifetimes of E1and E GS respectively.Due to the small∆com-pared to the barrier height between the atom and the source/drain contact,we expectϕ∼1.Together with ∆=1meV and T K∼2.7K(for sample H67)and∆=2meV and T K∼6K(for sample J17),Eq.2yields k B T K(∆)/k B T K(∆=0)=0.4and k B T K(∆)/k B T K(∆= 0)=0.3respectively.We can thus conclude that the rela-tively high∆,which separates E GS and E1well in energy, will certainly quench valley-stateﬂuctuations to a certain degree but is not expected to reduce T K to a level that Valley eﬀects become obscured.Valley Kondo density of statesHere,we explain in some more detail the relation be-tween the density of states induced by the Kondo eﬀects and the resulting current.The Kondo density of states (DOS)has three main peaks,see Fig.1a.A central peak at E F=0due to processes without valley-stateﬂip and two peaks at E F=±∆due to processes with valley-state ﬂip,as explained in the main text.Even a small asym-metry(ϕclose to1)will split the Valley Kondo DOS into an SU(2)-and an SU(4)-part[3],indicated in Fig1b in black and red respectively.The SU(2)-part is positioned at E F=0or E F=±∆,while the SU(4)-part will be shifted to slightly higher positive energy(on the order of T K).A voltage bias applied between the source and FIG.1:(a)dI SD/dV SD as a function of V SD in the Kondo regime(at395mV G)of sample J17.The substructure in the Kondo resonances is the result of a small diﬀerence between ΓE1andΓGS.This splits the peaks into a(central)SU(2)-part (black arrows)and two SU(4)-peaks(red arrows).(b)Density of states in the channel as a result ofϕ(=ΓE1/ΓGS)<1and applied V SD.drain leads results in the Kondo peaks to split,leaving a copy of the original structure in the DOS now at the E F of each lead,which is schematically indicated in Fig.1b by a separate DOS associated with each contact.The current density depends directly on the density of states present within the bias window deﬁned by source/drain (indicated by the gray area in Fig1b)[4].The splitting between SU(2)-and SU(4)-processes will thus lead to a three-peak structure as a function of V SD.Figure.1a has a few more noteworthy features.The zero-bias resonance is not positioned exactly at V SD=0, as can also be observed in the transport data(Fig1c of the main article)where it is a few hundredµeV above the Fermi energy near the D0charge state and a few hundredµeV below the Fermi energy near the D−charge state.This feature is also known to arise in the Kondo strong coupling limit[5,6].We further observe that the resonances at V SD=+/-2mV diﬀer substantially in magnitude.This asymmetry between the two side-peaks can actually be expected from SU(4)Kondo sys-tems where∆is of the same order as(but of course al-ways smaller than)the energy spacing between E GS and。

Understanding the Properties of Magnetic Materials

Understanding the Properties ofMagnetic MaterialsMagnetic materials have fascinated humans for centuries. From the mysterious lodestone that could attract iron to modern-day magnets used in a wide range of applications, magnetic materials have found their way into our daily lives. Understanding the properties of magnetic materials is essential for developing new applications and improving existing ones. In this article, we will explore the fundamental properties of magnetic materials and their relevance in various fields.Let us start with the basics. Magnetic materials are materials that are capable of generating a magnetic field. They can be classified into two categories: ferromagnetic and paramagnetic materials. Ferromagnetic materials, such as iron, cobalt, and nickel, exhibit a strong magnetic field, even in the absence of an external magnetic field. They also retain their magnetization even after the external field is removed. On the other hand, paramagnetic materials, such as aluminum, copper, and platinum, exhibit a weak magnetic field when exposed to an external magnetic field. However, they do not retain any magnetization once the external field is removed.Magnetic materials exhibit a unique property known as hysteresis. Hysteresis refers to the phenomenon in which the magnetic properties of a material depend on the history of magnetic fields it has been exposed to. The hysteresis curve represents the magnetization of the material as a function of the applied magnetic field. The area enclosed by the hysteresis curve represents the energy losses within the material. This phenomenon is important in the development of magnetic materials for power applications such as motors and transformers.The properties of magnetic materials are also affected by temperature. The degree of magnetization of ferromagnetic materials decreases as the temperature increases above a critical temperature known as the Curie temperature. Above this temperature, ferromagnetic materials become paramagnetic. The Curie temperature also plays a crucialrole in the development of magnetic materials for data storage applications such as magnetic tapes and hard disks.Another significant property of magnetic materials is their magnetic anisotropy. Magnetic anisotropy refers to the directionality of the magnetic properties of a material. The magnetic anisotropy of a material can be induced by an external magnetic field, uniaxial stress, or crystallographic structure. Magnetic anisotropy plays a crucial role in the development of magnetic materials for applications such as magnetic data storage, magnetic sensors, and magnetic actuators.The magnetic properties of materials can be controlled by manipulating their crystallographic structure. The crystallographic structure of a material affects the magnetic properties due to the interaction of electrons and the crystal lattice. The properties of magnetic materials can also be influenced by introducing impurities or alloys into the material. This process is known as doping and is commonly used to improve the magnetic properties of materials for various applications.In conclusion, understanding the properties of magnetic materials is critical for developing new technologies and improving existing ones. The fundamental properties of magnetic materials such as hysteresis, magnetic anisotropy, and temperature dependence are essential in the development of magnetic materials for various applications. The manipulation of crystallographic structure, the introduction of impurities and alloys, and other techniques have enabled researchers to improve the magnetic properties of materials for specific applications. With the continued development of magnetic materials, we can look forward to new and improved technologies that will enhance our daily lives.。

钕铁硼永磁材料制造流程中气流磨的作用

钕铁硼永磁材料制造流程中气流磨的作用In the manufacturing process of neodymium iron boron permanent magnets, gas jet milling plays an important role.在钕铁硼永磁材料的制造过程中，气流磨具有重要的作用。

Gas jet milling is a type of mechanical milling where high-speed compressed gas is used to accelerate particles and achieve particle size reduction. This technique allows for fine grinding of the raw materials used in the production of neodymium iron boron magnets.气流磨是一种机械磨削的方法，利用高速压缩气体加速颗粒，并实现颗粒尺寸的减小。

这种技术可以对制造钕铁硼磁体所使用的原材料进行细致的研磨。

The main purpose of gas jet milling in the manufacturing process of neodymium iron boron magnets is to reduce the particle size of the raw materials. By reducing theparticle size, we can increase the surface area available for chemical reactions and improve the homogeneity of themixture. This has a direct impact on the magnetic properties and performance of the final product.气流磨在制造钕铁硼磁体的过程中主要目的是减小原材料的颗粒尺寸。

磁斯格明子在钉扎作用下的动力学研究进展

Vol. 1, No. 1 第1卷第1期Science and Engineering科学与工程December, 2022 2022年12月基金项目: 西交利物浦大学Key Programme Special Fund (Grant No. KSF-E-22); Research Enhancement Fund (Grant No. REF17-1-7).*通信作者: 于昊, Hao.Y ***********.cn收稿日期: 2022-09-28; 接受日期: 2022-10-24; 在线出版日期: 2023-01-05磁斯格明子在钉扎作用下的动力学研究进展蒋韫希, 于昊*西交利物浦大学物理系, 江苏苏州 215123摘要: 磁斯格明子由于其具有拓扑保护、尺寸小、驱动电流低的优势，有望应用于下一代存储和计算器件，例如赛道存储、逻辑计算和神经计算器件。

室温下磁斯格明子的发现也为实现基于磁斯格明子的计算和存储器件奠定了基础。

缺陷和杂质等在真实材料中不可避免，这些天然的钉扎中心会对磁斯格明子的动力学，包括临界驱动电流、霍尔角度等产生重要影响。

关于薄膜中室温磁斯格明子的工作表明，钉扎的影响在室温下会非常大。

因此，研究不同温度下的钉扎效应和磁斯格明子-钉扎间的相互作用，对研究磁斯格明子在实际器件中的动力学和实现室温磁斯格明子自旋器件非常重要。

此外，利用这些作用也可人工引入钉扎中心以操控磁斯格明子的运动。

本文介绍了磁斯格明子的动力学模型，特别是在有限温环境、钉扎作用下的理论模型，以及数值模拟。

同时，简要综述了最近关于钉扎和磁斯格明子相互作用的一些研究工作；并展望了该领域的研究方向。

通过替换或增加原子、设置空缺、改变材料厚度或弯曲度、改变磁性参数等方式引入钉扎时，可使磁斯格明子运动时的霍尔角发生变化，也可将磁斯格明子固定在某一区域，或沿着特定轨道运动，克服室温下热扰动，有助于实现室温下磁斯格明子自旋器件。

21年考研真题英语答案

21年考研真题英语答案来自21年考研真题的英语部分，本文将提供详细的答案解析以帮助考生更好地理解和准备考试。

以下将按照题目的顺序给出解答，并提供相关的解题思路和对答案的详细解析。

阅读理解部分：Passage 1:1. A解析：根据第一段的句子"Physicists have identified the source of "tricritical” magnetic behavior in a material that could benefit next-generation computing." 可知，物理学家已经找到了下一代计算机中受益的材料的“三重临界”磁性行为的来源。

根据上下文也可以判断出这是一项新的发现。

2. C解析：根据第三段 "This is the first time that a new type of magnetic behavior has been predicted theoretically and then discovered experimentally." 可知，从理论上预测然后通过实验证明这种新型磁性行为是第一次。

所以选C。

3. B解析：根据第六段 "These are intriguing discoveries that will help unlock novel electric and magnetic effects." 可知，这些都是令人感兴趣的发现，将有助于揭示新的电磁效应。

4. D解析：根据最后一段的最后一句 "The effort could also create a path to finding other novel materials with potentially useful properties." 可知，此举还可以为发现其他具有潜在有用性能的新材料铺平道路。

基因毒性杂质限度指南

基因毒性杂质限度指南（中英文对照）London, 28 June 2006CPMP/SWP/5199/02EMEA/CHMP/QWP/251344/2006TABLE OF CONTENTS 目录EXECUTIVE SUMMARY 内容摘要............................................................................. .. (3)1. INTRODUCTION 介绍............................................................................. . (3)2. SCOPE 范围 ............................................................................ (3)3. LEGAL BASIS法律依据............................................................................. . (3)4. TOXICOLOGICAL BACKGROUND 毒理学背景 (4)5. RECOMMENDATIONS 建议............................................................................. (4)5.1 Genotoxic Compounds With Sufficient Evidence for a Threshold-Related Mechanism具有充分证据证明其阈值相关机理的基因毒性化合物 (4)5.2 Genotoxic Compounds Without Sufficient Evidence for a Threshold-Related Mechanism不具备充分证据支持其阈值相关机理的基因毒性化合物 (5)5.2.1 Pharmaceutical Assessment药学评价............................................................................. .. (5)5.2.2 Toxicological Assessment毒理学评价............................................................................. (5)5.2.3 Application of a Threshold of Toxicological Concern 毒理学担忧阈值应用 (5)5.3 Decision Tree for Assessment of Acceptability of Genotoxic Impurities基因毒性杂质可接受性评价决策树............................................................................. . (7)REFERENCES. 参考文献............................................................................. .. (8)EXECUTIVE SUMMARY 内容摘要The toxicological assessment of genotoxic impurities and the determination of acceptable limits for such impurities in active substances is a difficult issue and not addressed in sufficient detail in the existing ICH Q3X guidances. The data set usually available for genotoxic impurities is quite variable and is the main factor that dictates the process used for the assessment of acceptable limits. In the absence of data usually needed for the application of one of the established risk assessment methods, i.e. data from carcinogenicity long-term studies or data providing evidence for a threshold mechanism of genotoxicity, implementation of a generally applicable approach as defined by the Threshold of Toxicological Concern (TTC) is proposed.A TTC value of 1.5 μg/day intake of a genotoxic impurity is considered to be associated with an acceptable risk (excess cancer risk of <1 in 100,000 over a lifetime) for most pharmaceuticals. From this threshold value, a permitted level in the active substance can be calculated based on the expected daily dose. Higher limits may be justified under certain conditions such as short-term exposure periods.基因毒性杂质的毒理学评估和这些杂质在活性药物中的可接受标准的测定是一件困难的事情，并且在现有的ICH Q3X指南中也没有详细的规定。

铁矿石中英文对照

铁矿石的分类Iron ore classification按照矿物组分、结构、构造和采、选、冶及工艺流程等特点，可将铁矿石分为自然类型和工业类型两大类。

According to mineral composition,structure,construction and mining, metallurgical and technological process and other features,can be dividedinto natural types of iron ore and industrial types of two categories.1.自然类型1natural types1)根据含铁矿物种类可分为：磁铁矿石、赤铁矿石、假象或半假象赤铁矿石、钒钛磁铁矿石、褐铁矿石、菱铁矿石以及由其中两种或两种以上含铁矿物组成的混合矿石。

1)according to the iron ore types can be divided into:magnetite,hematite, false or half pseudomorph,vanadium-titanium magnetite ore,hematite,siderite and limonite ore from which two or more than two kinds of minerals containing composition of mixed ore.2)按有害杂质(S、P、Cu、Pb、Zn、V、Ti、Co、Ni、Sn、F、As)含量的高低，可分为高硫铁矿石、低硫铁矿石、高磷铁矿石、低磷铁矿石等。

2)according to the harmful impurities(S,P,Cu,Pb,Zn,V,Ti,Co,Ni,Sn,F, As)content,can be classified as high sulfurous iron ore,sulphur iron ore,high phosphorus iron ore,low phosphorus iron ore.3)按结构、构造可分为浸染状矿石、网脉浸染状矿石、条纹状矿石、条带状矿石、致密块状矿石、角砾状矿石，以及鲕状、豆状、肾状、蜂窝状、粉状、土状矿石等。

欧洲药典7.5版

EUROPEAN PHARMACOPOEIA 7.5
INDEX
To aid users the index includes a reference to the supplement in which the latest version of a text can be found. For example : Amikacin sulfate...............................................7.5-4579 means the monograph Amikacin sulfate can be found on page 4579 of Supplement 7.5. Note that where no reference to a supplement is made, the text can be found in the principal volume.
English index ........................................................................ 4707
Latin index ................................................................................. 4739
EUROPEAN PHARMACOPபைடு நூலகம்EIA 7.5
Index
Numerics 1. General notices ................................................................... 7.5-4453 2.1.1. Droppers...................

锂离子电池原料中磁性杂质检测

第34卷第3期2020年5月天津化工Tianjin Chemical IndustryVo1.34No.3May2020•分析与测试•锂离子电池原料中磁性杂质检测崔雪红,王淑霞,张明春(天津市捷威动力工业有限公司，天津300384)摘要:锂离子电池原料中存在的微量金属杂质对锂离子电池来说是重大安全隐患，可导致严重的后果。

准确检测锂离子电池原料中磁性杂质含量是锂离子电池需要关注的问题。

利用高强磁铁吸附、ICP-OES发射光谱仪定量测试，可准确检测锂离子电池原料中磁性杂质。

关键词：磁性杂质；ICP-OES；锂离子电池材料doi:10.3969/j.issn.l008-l267.2020.03.020中图分类号:TQ042文献标志码:A文章编号:1008-1267(2020)03-0059-03Detection of magnetic impurities in lithium1on battery materialsCUI Xue-hong,WANG Shu-xia,ZHANG Ming-chun(Tianjin EV Energies co.,Ltd,Tianjin300384)Abstract: Trace metal impurities in the raw materials of lithium ion batteries are major potential safety hazards for lithium ion batteries and can lead to serious consequences.Accurate detection of magnetic impurity content in raw materials of lithium ion batteries is a concern for lithium ion batteries.Magnetic impurities in lithium ion battery raw materials can be accurately detected by high-strength magnet adsorption and ICP-OES emission spectrometer quantitative testing.Key words：magnetic impurities;ICP-OES;lithium ion battery material众所周知，2006年日本索尼笔记本电池发生起火事件,究其原因，是其生产过程中混入了微细金属粉末引起发热或短路所致。

钢铁是怎样炼成的在车站干活读后感

钢铁是怎样炼成的在车站干活读后感英文回答：How Steel is Made and My Reflection on Working at the Station.Steel is a versatile and essential material that is widely used in various industries, from construction to manufacturing. The process of making steel involves several steps, each crucial in transforming raw materials into the strong and durable metal we know.The first step in steel production is the extraction of iron ore. Iron ore is mined from the earth's crust and then transported to steel mills for further processing. Once at the steel mill, the iron ore undergoes a series of crushing, grinding, and magnetic separation processes to remove impurities and concentrate the iron content.The next step is the conversion of iron ore into iron.This is achieved through a process called smelting, where the iron ore is heated in a blast furnace with coke (a form of carbon) and limestone. The intense heat causes the iron ore to melt, and the carbon reacts with oxygen to remove impurities, resulting in molten iron.The molten iron is then further processed in a basic oxygen furnace (BOF) or an electric arc furnace (EAF) to remove any remaining impurities and to adjust the carbon content. In the BOF process, pure oxygen is blown into the molten iron, which oxidizes impurities and reduces the carbon content. In the EAF process, electricity is used to melt the iron and remove impurities.After the desired carbon content is achieved, various alloying elements such as manganese, nickel, and chromium can be added to enhance the steel's properties. Once the composition is finalized, the molten steel is cast into different shapes, such as slabs, billets, or ingots, depending on the intended use.The final step in steel production is the shaping andfinishing of the steel. This can involve processes such as rolling, forging, or machining to achieve the desired shape and dimensions. The steel may also undergo heat treatment processes, such as annealing or quenching, to improve its strength and hardness.Reflecting on my experience of working at the station, I have gained a deeper appreciation for the complexity and importance of the steelmaking process. The coordinated efforts of countless individuals, from miners to furnace operators, are required to produce high-quality steel that meets the demands of modern society.Working at the station has also exposed me to the challenges and hazards associated with steel production. The extreme temperatures, heavy machinery, and potentially harmful substances require strict adherence to safety protocols and constant vigilance.Overall, my time at the station has given me a newfound respect for the steel industry and the dedication of the workers involved in its production. Steel truly is aremarkable material that has shaped the world we live in, and I am grateful for the opportunity to have witnessed its creation firsthand.中文回答：钢铁是怎样炼成的以及在车站工作的个人感悟。

Magnetic Nanoparticles

Magnetic NanoparticlesNanoparticles, or particles with sizes in the nanometer range, are growing in importance in many fields of science and technology, including medicine, electronics, and environmental science. Magnetic nanoparticles are a particularly useful type of nanoparticle that have many potential applications. In this article, we will explore the properties and potential applications of magnetic nanoparticles.Properties of Magnetic nanoparticles are made from magnetic materials such as iron, nickel, and cobalt. They can have a variety of shapes, including spherical, rod-like, and disk-shaped. The magnetic properties of nanoparticles depend on their size and composition. When a magnetic field is applied to magnetic nanoparticles, they become magnetized, meaning that they develop a magnetic moment aligned with the direction of the field. This property can be exploited in many applications.One important property of magnetic nanoparticles is their ability to be manipulated using a magnetic field. This makes them useful in a wide range of applications, from biomedical imaging to environmental remediation. In addition, magnetic nanoparticles can be functionalized, or coated with other materials such as polymers or proteins, to enhance their properties or to target specific biological molecules or cells.Applications of Biomedical ApplicationsOne of the most promising applications of magnetic nanoparticles is in biomedicine. Magnetic nanoparticles have the potential to revolutionize the diagnosis and treatment of diseases by providing non-invasive imaging, targeted drug delivery, and magnetic hyperthermia. Magnetic nanoparticles can be functionalized with a variety of biomolecules, such as antibodies, peptides, or nucleic acids, to target specific cells or tissues. This targeted delivery of drugs or imaging agents can reduce side effects and increase the efficiency of treatment.Magnetic nanoparticles can also be used for magnetic hyperthermia, a treatment in which the nanoparticles are heated using an alternating magnetic field. This localizedheating can kill cancer cells or bacteria without damaging healthy tissue. In addition, magnetic nanoparticles can be used for magnetic resonance imaging (MRI), a non-invasive imaging technique that can provide detailed images of internal structures.Environmental ApplicationsMagnetic nanoparticles also have potential applications in environmental science. They can be used for the removal of pollutants from water or soil. Magnetic nanoparticles can be functionalized with materials such as activated carbon or zeolites to increase their adsorption capacity. Once the pollutants are adsorbed onto the magnetic nanoparticles, they can be easily removed using a magnetic field.In addition, magnetic nanoparticles can be used to treat contaminated soils or sediments. They can be used to remove heavy metals, organic contaminants, or radioactive substances. The nanoparticles can be functionalized with materials such as humic acid or chitosan to increase their capacity for binding contaminants.Electronics and Data StorageMagnetic nanoparticles also have potential applications in electronics and data storage. Magnetic nanoparticles can be used in magnetic information storage devices such as magnetic hard drives, magnetic random access memory (MRAM), and magnetic tapes. The small size of the nanoparticles allows for higher density storage, while their magnetic properties make them ideal for reading and writing data.ConclusionMagnetic nanoparticles are a versatile and promising type of nanoparticle with many potential applications. Their magnetic properties make them useful in a variety of fields, including biomedicine, environmental science, and electronics. As research into magnetic nanoparticles continues, we can expect to see exciting new applications emerge.。

多肽合成杂质避免方法

多肽合成杂质避免方法Peptide synthesis is a crucial technique in the field of biochemistry, allowing researchers to produce custom peptides for various purposes. However, one common issue that arises during peptide synthesis is the presence of impurities. These impurities can result in inaccurate research findings and wasted resources, making it essential to have effective methods for avoiding impurities in peptide synthesis.多肽合成是生物化学领域中的一项关键技术，它使研究人员能够为各种目的生产定制的多肽。

然而，在多肽合成过程中经常会出现的一个问题是存在杂质。

这些杂质可能导致不准确的研究结果和资源浪费，因此有必要拥有有效的方法来避免多肽合成中的杂质。

One approach to minimizing impurities in peptide synthesis is to carefully select high-quality reagents and solvents. By using pure chemicals and solvents, researchers can reduce the likelihood of impurities contaminating the synthesized peptides. Additionally, proper storage and handling of reagents and solvents can also help prevent impurities from compromising the synthesis process.减少多肽合成中杂质的一种方法是精心选择高质量的试剂和溶剂。

钛铁矿的质量标准

钛铁矿的质量标准Titanium iron ore is a valuable resource that is used in various industries, from aerospace to manufacturing. Its quality standards play a crucial role in determining its value and usability. The quality of titanium iron ore is typically evaluated based on its chemical composition, physical properties, and impurities present.钛铁矿是一种宝贵的资源，被广泛应用于航空航天到制造等各个领域。

其质量标准对于决定其价值和可用性起着至关重要的作用。

钛铁矿的质量通常根据其化学成分、物理性质和存在的杂质来评估。

Chemical composition is one of the key factors in determining the quality of titanium iron ore. The percentage of titanium, iron, and other elements present in the ore can significantly impact its overall quality. The ideal chemical composition for titanium iron ore varies depending on its intended use, with specific industries requiring different levels of purity and composition.化学成分是确定钛铁矿质量的关键因素之一。

我的愿望可控核聚变英语作文

我的愿望可控核聚变英语作文英文回答：Nuclear fusion has the potential to revolutionize the world's energy supply by providing a clean, safe, and virtually limitless source of power. However, achieving controlled nuclear fusion has been a challenging scientific and engineering endeavor for decades.The process of nuclear fusion involves combining two atomic nuclei to form a heavier nucleus, releasing a tremendous amount of energy. The most common approach to controlled fusion is to use a tokamak, a doughnut-shaped device that confines a plasma of hydrogen isotopes in a magnetic field. By heating the plasma to extremely high temperatures, the atomic nuclei overcome theirelectrostatic repulsion and fuse together.To achieve controlled fusion, several key conditions must be met:The plasma must be heated to temperatures of hundredsof millions of degrees Celsius.The plasma must be confined for a sufficiently long period of time to allow for fusion reactions to occur.Impurities in the plasma must be minimized to reduce energy losses.Researchers have made significant progress indeveloping technologies to meet these conditions. Advancesin plasma heating, magnetic confinement, and impuritycontrol have brought us closer to the realization of controlled nuclear fusion.The benefits of controlled nuclear fusion are numerous. It would provide a virtually inexhaustible source of energy, reducing our reliance on fossil fuels and mitigatingclimate change. Fusion power plants would be inherently safe, as they do not produce radioactive waste or the riskof a runaway chain reaction. Additionally, fusiontechnology could lead to breakthroughs in other fields, such as materials science and medical imaging.While the path to controlled nuclear fusion is still fraught with challenges, the potential rewards are immense. Continued research and development in this field are essential to unlock the transformative power of fusion energy.中文回答：可控核聚变是一种能够提供清洁、安全、近乎无限的能源，从而彻底改变全球能源格局的技术。

磷酸铁锂磁性杂质对电池自放电的影响

磷酸铁锂磁性杂质对电池自放电的影响杨续来;刘成士;谢佳;徐小明【摘要】通过磁性分析研究了3种商品化磷酸铁锂(LiFePO4)的磁性杂质含量.LiFePO4中含有磷化铁(Fe2P)、三氧化二铁(Fe2O3)及单质铁等磁性杂质；磁性杂质会提高成品电池的自放电率.在实验条件下,经328 K储存后,磁性杂质物质的量含量为1.63％的LiFePO4制成的电池,自放电率约为磁性杂质含量为0.04％的LiFePO4制成的电池的5.6倍.%Magnetic impurities content in 3 kinds of commercialized lithium iron phosphate(LiFePO4) was investigated with magnetic measurements. The magnetic impurities such as ferrous phosphide(Fe2P),ferric oxide(Fe2O3) and metallic iron were existed in LiFePO4.The magnetic impurities would increase the self-discharge rate of finished battery.In experimental conditions, after stored under 328 K, the self-discharge rate of battery prepared with LiFePO4 of 1.63% (molar content) magnetic impurities was about 5.6 times than the one with 0.04% magnetic impurities.【期刊名称】《电池》【年(卷),期】2012(042)006【总页数】4页(P314-317)【关键词】磷酸铁锂(LiFePO4);磁性分析;磁化曲线;自放电【作者】杨续来;刘成士;谢佳;徐小明【作者单位】安徽省动力锂离子电池工程技术研究中心,合肥国轩高科动力能源有限公司,安徽合肥230011;安徽省动力锂离子电池工程技术研究中心,合肥国轩高科动力能源有限公司,安徽合肥230011;安徽省动力锂离子电池工程技术研究中心,合肥国轩高科动力能源有限公司,安徽合肥230011;安徽省动力锂离子电池工程技术研究中心,合肥国轩高科动力能源有限公司,安徽合肥230011【正文语种】中文【中图分类】TM912.9在磷酸铁锂(LiFePO4)的合成过程中,会伴随生成少量的γ-Fe2O3、FeP、Fe2P 及Fe2P2O7等杂质[1],单质铁也会在还原性气氛,如CO、H2等气氛下,在500～700℃经Fe3+的还原而生成[2]。

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a r X i v :0807.0769v 2 [c o n d -m a t .s u p r -c o n ] 8 J u l 2008Short note on magnetic impurities in SmFeAsO 1−x F x (x=0,0.07)compounds revealedby zero-ﬁeld 75As NMRA.A.Sidorenko ∗and R.De RenziDipartimento di Fisica e Unit`a CNISM,Universit`a degli Studi di Parma,Vialle delle Scienze,7A,43100Parma,ItalyA.Martinelli and A.PalenzonaCNR-INFM-LAMIA Artiﬁcial and Innovative Materials Laboratory,Corso Perrone 24,16152Genova,Italy(Dated:July 8,2008)We have performed zero-ﬁeld 75As nuclear magnetic resonance study of SmFeAsO 1−x F x (x=0,0.07)polycrystals in a wide frequency range at various temperatures.75As resonance line was found at around 265MHz revealing the formation of the intermetallic FeAs clusters in the new layered superconductors.We have also demonstrated that NMR is a sensitive tool for probing the quality of these materials.The layered rare-earth metal oxypnictides ROFeAs (where R -rare-earth ions)have attracted a great at-tention after the discovery of the superconductivity in the iron-based LaFeAsO 1−x F x .[1]Replacement of La by other rare-earth ions leads to a large increase in T C from 26K in LaFeAsO 1−x F x to T C >50K in RFeAsO 1−x F x with R =Nd,Pr,Sm,and Gd.[2,3,4,5,6]However,Nowik and Felner [7]using M¨o ssbauer spectroscopy have recently found that most RFeAsO 1−x F x compounds con-tain foreign magnetic Fe-As phases such as Fe 2As,FeAs 2and FeAs,regardless the preparation method in amounts which might reach even 50%.Although large amounts are easily detected by X-ray diﬀraction (XRD)quanteties below 5-10%may escape this standard characteriza-tion and inﬂuency heavily magnetic properties as seen by macroscopic magnetization/susceptibility.In princi-ple,this fact can lead to wrong conclusions on magnetic and related properties of the newly discovered supercon-ductors.In this work,we investigate SmFeAsO 1−x F x com-pounds with x=0and 0.07addressing speciﬁcally the issue of intermetallic magnetic FeAs clusters with the magnetic transition temperature 77K[8]by means of zero-ﬁeld 75As nuclear magnetic resonance (NMR).NMR spectra were collected with the home-built broadband fast-averaging NMR spectrometer HyReSpect[9]on a tuned probe circuit.The zero-ﬁeld spectra were obtained in the frequency range 200-350MHz by means of a stan-dard optimized Θ−τ−Θspin-echo pulse sequence,plot-ting point by point the amplitude at zero frequency shift of the Fast Fourier Transform of each echo as a func-tion of transmission frequency.The NMR spectra are always corrected for NMR sensitivity,rescaling their am-plitudes by ω2.Details on the samples preparation as well as on their characterization by means of Rietveld re-ﬁnment of XRD data,scanning electron microscopy ob-servation,transmission electron microscope analysis,re-sistivity and magnetization measurements can be found21(b)very similar spectrum was found in the doped sam-ple SmFeAsO0.93F0.07as well.It should be mentioned that the position and FWHM of these lines do not de-pend on the doping level,that is,the resonance lines are the very same in both normal(undoped)and supercon-ducting(doped)phases.In addition,by applying an ex-ternal magneticﬁeld the resonance line is shifted towards high frequencies,indicating a positive hyperﬁneﬁeld on nuclei,as expected for the As ions.[11]The existence of the resonance in zero external magneticﬁeld and low ap-plied radio-frequency power indicate that the NMR signal is due to the enhancement of the radio-frequencyﬁeld by domain wall motion[12,13]revealing the formation of the magnetic FeAs clusters(maybe even of the nanoscopic di-mension)in SmFeAsO1−x F x compounds and,therefore, conﬁrming the results of M¨o ssbauer spectroscopy.[7][1]Y.Kamihara,T.Watanabe,M.Hirano,and H.Hosono,J.Am.Chem.Soc.130,3296(2008).[2]Z.-A.Ren,J.Yang,W.Lu,W.Yi,X.-L.Shen,Z.-C.Li,G.-C.Che,X.-L.Dong,L.-L.Sun,F.Zhou,et al., Europhys.Lett.82,57002(2008).[3]R.H.Liu,G.W.adn T.Wu,D.F.Fang,H.Chen,S.Y.Li,K.Liu,Y.L.Xie,X.F.Wang,R.L.Yang,L.Ding, et al.(2008),arXiv:0804.2105[cond-mat.supr-con].[4]Z.-A.Ren,W.Lu,J.Yang,W.Yi,X.-L.Shen,Z.-C.Li,G.-C.Che,X.-L.Dong,L.-L.Sun,F.Zhou,et al.,Chin.Phys.Lett.25,2215(2008).[5]J.Yang,Z.-C.Li,W.Lu,W.Yi,X.-L.Shen,Z.-A.Ren,G.-C.Che,X.-L.Dong,L.-L.Sun,F.Zhou,et al.,Su-percond.Sci.Technol.21,82001(2008).[6]X.H.Chen,T.Wu,G.Wu,R.H.Liu,H.Chen,andD.F.Fang,Nature453,761(2008).[7]I.Nowik and I.Felner(2008),arXiv:0806.4078[cond-mat.supr-con].[8]S.K.Kulshreshtha and P.Raj,J.Phys.F:Metal.Phys.9,2253(1979).[9]G.Allodi,A.Banderini,R.De Renzi,and C.Vignali,Rev.Sci.Instrum.76,83911(2005).[10]A.Martinelli,M.Ferretti,P.Manfrinetti,A.Palenzona,M.Tropeano,M.R.Cimberle,C.Ferdeghini,R.Valle, M.Putti,and A.S.Siri(2008),arXiv:0806.2205[cond-mat.supr-con].[11]A.J.Freeman and R.E.Watson,in Magnetism,editedby G.T.Rado and H.Suhl(Academic Press,New York and London,1965),vol.2A,p.168.[12]E.A.Turov and M.P.Petrov,Nuclear Magnetic Res-onance in Ferro-and Antiferromagnets(Halsted,New York,1972).[13]A.M.Portis and R.H.Lindquist,in Magnetism,editedby G.T.Rado and H.Suhl(Academic Press,New York and London,1965),vol.2A,p.357.。