亚纳米金属团簇的磁性

Ef
Decrease of moment due to band narrowing, W vs sqrt(Z) ^^^^ Enhance of moment due to level shift of bands
32
Surface: Dipole and Potential
33
Giant Surface Spin Moment
1G
-20
18
2P 1F
14
6
-40
-60
1D
10
2S
2
-80
1S, 1P, 1D+2S, 1F, 2P, 1G ..
1P
-100
6
1S
0
2
10
20
30
40
50
60
Number of electrons
5
Nanocluster Structure Geometry
Too small for diffraction; too large for spectroscopy
3
Abundance Spectra
4
Magic Number and Quantum Confinement
0
Energy of each electron
• Magic population in cluster size (n) (Cu,Ag,Au)n+: 3, 9, 21, 35, 41, 59 .. (Cu,Ag,Au)n- : 7, 19, 33, 39, 57 .. • Magic Ne: 2, 8, 20, 34, 40, 58 .. • Increent of Ne and states assigned 2, 6, 12, 14, 6, 18 ..
28
Interests in Cluster Magnetism
• • • • • Enhance/adjust of moments; Onset of magnetism in nonmagnetic metals; Moment variation over one cluster; Release of orbital quenching; Enhance of anisotropy;
20
Fe Clusters on HOPG
21
Fe Clusters in Carbon Black
22
Experiments on Ni-Fe-Co Clusters
Moment Atom Co Co Co Co Fe Fe Fe Fe Ni Method Stern-G on Si in polymer on Au Stern-G Stern-G on HOPG in Carbon Stern-G Size 115 ~50-100 1.5-1.9 nm 300-12000 10-25 25-700 2.1 nm 2-6 nm 3-700 2.1 2.1 1.7 - 1.9 ML/MS or ML K (eV)
Cluster Size (atoms)
8
Findings in Cluster Magnetism and Interests
• Theory of cluster magnetism, G.M. Pastor,
in Atomic clusters and nanoparticles, Eds. Guet, C.; Hobza, P.; Spiegelman, F.; David, F., Springer Series: Les Houches - Ecole d'Ete de Physique Theorique (Les Houches 2-28 July 2000), Vol. 73 (2001)
– Orbit correlation – Spin orbit coupling
40
Magnetism of Crystals: Orbital Quench
6
Nanocluster Structure Geometry
7
Trend of Evolution - Ratio of Inertia
Ratio of Inertia and Structure Evolution
1.0
0.8
0.6
0.4
0.2
I1/I3 I2/I3 ICO MIC TIC
0.0 10 20 30 40 50 60
• Free
– accurate measuring of cluster size
• Supported or Embedded
– accessible by traditional techniques – good for measuring various magnetic properties, e.g., spin vs orbital moment, anisotropy, hyperfine field, etc – compatible with application purposes
LSDA spin moment , and surface core level shift of Ni films (FLAPW) System Bulk (100) center (111) center (111) surface (100) surface (111) monolayer (100) monolayer Z 12 12 12 9 8 6 4 (B) 0.561 0.619 0.613 0.625 0.675 0.892 1.014 Shift(eV)
11
Stern-Gerlach Experimental Setup
12
Intrinsic Moment by Stern-Gerlach Setup
13
Moment of Free Ni Clusters
14
Moment of Free Ni Clusters
15
Co Clusters on Si
– Orbit correlation – Spin orbit coupling
36
Quantum Confine Effect on Magnetism
37
Quantum wenku.baidu.comonfine Effect on Magnetism
38
LSDA Moment of Ni Clusters
2.0
Moment (Bohr Magneton/atom)
29
Basic Ingredients in cluster magnetism
• Surface enhancement
– Interatomic hopping – Orbital energy shift
– Spin exchange
• Quantum confinement
– Interatomic hopping – Orbital energy shift
1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 10 20 30 40 50
Apsel et al Knickelbein Reuse et al Reddy et al Fujima et al
60
Cluster Size (atoms)
39
Basic Ingredients in cluster magnetism
2
Cluster Structure and Magic Population
The Physics of simple metal clusters: experimental aspects and models
W. A. de Heer, Rev. Mod. Phys. 65, 615, 1993
• Surface enhancement
– Interatomic hopping – Orbital energy shift
– Spin exchange
• Quantum confinement
– Interatomic hopping – Orbital energy shift
• Orbital polarization vs quench
26
Colloidal Pd Clusters
27
Experiments on Other Clusters
Moment Atom Al-Cr-V Ru Rh Pd Pd Pd Size 9-99 10-115 12-32 13-120 2.4 nm 4-14 nm Method Stern-G Stern-G Stern-G Stern-G colloidal evap. aggr. 0.000 0.000 1.1 - 0.4 0.000 0.02emu/ g Only (100) M L/ M S or M L K (eV)
• m = 2.1 B/atom Pan et al. Nano Lett. 5, 87 (2005)
16
Co Clusters in Polymers
17
Co Clusters on Au
18
Moment of Free Fe Clusters
19
Moment of Free Fe Clusters
Ef
Decrease of moment due to band narrowing W vs sqrt(Z)
31
Mangetism of Surfaces: Enhancement
Basic fact for Fe, Co, and Ni spin up band fully filled spin down band > half filled
0.291 0.354
34
Z(Coordination) Model
P.J.Jessen and K.H.Bennemann, Z. Phys. D 35, 273 (1995)
= S i = S (Zi)
35
Basic Ingredients in cluster magnetism
• Surface enhancement
亚纳米金属团簇的磁性
王鼎盛（中国科学院物理研究所）
dswang@aphy.iphy.ac.cn
1
Contents
• • • • • • Cluster structure and magic population Findings in cluster magnetism and interests Magnetism of atoms, crystals and its surfaces Theoretical challenges in cluster magnetism Unified TB model of cluster magnetism Summary
• Orbital polarization vs quench
– Orbit correlation – Spin orbit coupling
30
Magnetism of Surfaces: Reduction
Basic fact for Fe, Co, and Ni spin up band fully filled spin down band > half filled
9
Magnetism from Atoms to Crystals
Nickel Spin Orbital Atom 2 B 3 B Cluster ? ? Surface Solid
0.6-1.0 B 0.6 B >0.05 B 0.05 B
10
Magnetic Experiments of Nano-clusters - Free, or Supported, or Embedded
– Interatomic hopping – Orbital energy shift
– Spin exchange
• Quantum confinement
– Interatomic hopping – Orbital energy shift
• Orbital polarization vs quench
0.37 0.2 - 0.1
500 58 - 51 8-2
5.4 - 2.6 3.1 - 2.2 1.5
0.18 B 22 - 7
1.8 - 0.7
23
Moment of Free Al-Cr-V-Pd Clusters
24
Moment of Free Ru-Rh-Pd Clusters
25
Aggregate of Evaporated Pd Clusters