1
Magnetic Nanoclusters
By: Adam Krause2/27/07
Physics 672
2
Nanocluster Quick Introduction
From a few atoms to several thousand atoms
High fraction of atoms on the surfaceDifferent elements form different bonds
and different nanocluster structures
3
A Few Types of Nanoclusters
Van der Waals Nanoclusters
Figure above from: Alonso, J. A., Structure and Properties of Atomic Nanoclusters, 2005
Binding energy: < 0.3 eV / atom
Balance between induced dipole force and quantum closed shell interaction
Noble gases form icosahedral Van der Waals clusters
4
A Few Types of Nanoclusters
Van der Waals Nanoclusters
Figure above from: Echt, O., et al., J. Chem. Soc. Faraday Trans., 86 (1990) 2411
The drops at 148 and 309 atoms correspond to completed icosahedra.
5
A Few Types of Nanoclusters
Ionic Nanoclusters
NaCl Cluster
Graph above from: Martin, T. P., Physics Reports, 273 (1996) 199
Bond Strength: 2-4 eV / atom Tend to form boxes
6
A Few Types of Nanoclusters
Metal clusters have complicated bonding that varies from metal to metal
Due to this variation the bond strength varies from around 0.5 eV to 3 eV per atom
Metal Nanoclusters
7
Laser Vaporization
Figure above from: Billas et al., J. Magn. Magn. Mater. 168 (1997) 64
Metal Nanoclusters Produced By Laser Vaporization
8
Stern-Gerlach Apparatus
Figure above from: Billas et al., J. Magn. Magn. Mater. 168 (1997) 64
9
Description of magnetic particles
10
Band Structure Evolution
Figure above from: Billas et al., J. Magn. Magn. Mater. 168 (1997) 64
Increasing Coordination Number
11
Magnetic Moment vs. Cluster Size
Figure above from: Billas et al., J. Magn. Magn. Mater. 168 (1997) 64
12
Closed Shell Cluster Size vs. Magnetic Moment Minima.
Table above from: Jensen, P. J., and K. H. Bennemann, Z. Phys. D. 35 (1995) 273
13
Magnetic Shell Model
bulk
bulkbulk
NNNxNNNN
100
1100)( (1)
ci
ciii qq
qqq
,,
)(2
1
(2)
Graphs from: Jensen, P. J., and K. H. Bennemann, Z. Phys. D. 35 (1995) 273
14
Magnetic Moment vs. Temperature
Fe
Ni
Co
Graphs from: Billas, M. L., A. Chatelain, and W. A. de Heer, Science 265 (1994) 1682
15
Monte Carlo Simulation of Magnetization vs. 1/Temp
Graph from: Binder, K., et al., J. Phys. Chem. Solids, 31 (1970) 391
16
Superparamagnetism
Magnetization Loops of Fe Nanoclusters
Graph from: Jackson, T. J., et al., J. Phys.: Condens. Matter, 12 (2000) 1399
17
Summary
Metal nanoclusters of an element behave differently than bulk matter of the same element.
d-orbital overlap reduces magnetic moment per atom. Metal nanoclusters exhibit magnetic shell phenomenon Metal nanoclusters do not lose their magnetization as
quickly above the Curie temp. Metal nanoclusters exhibit superparamagnetic
behavior. Superparamagnetism provides a theoretical minimum
size per bit in magnetic moment based memory systems.
18
References1. Alonso, J. A., Structure and Properties of Atomic Nanoclusters (Imperial College
Press, London, 2005).2. Echt, O., et al., J. Chem. Soc. Faraday Trans., 86 (1990) 24113. Martin, T. P., Physics Reports, 273 (1996) 1994. Dietz, T. G., et al., J. Chem. Phys., 74 (1981) 65115. Bondybey, V. E., and J. H. English, J. Chem. Phys., 76 (1982) 21656. Billas, M. L., A. Chatelain, and W. A. de Heer, J. Magn. Magn. Mater. 168
(1997) 647. Cox, D. M., et al, Phys. Rev. B., 32 (1985) 72918. Billas, M. L., A. Chatelain, and W. A. de Heer, Science 265 (1994) 16829. Jensen, P. J., and K. H. Bennemann, Z. Phys. D. 35 (1995) 27310. Billas, M. L., et al., Phys. Rev. Lett., 71 (1993) 406711. Binder, K., et al., J. Phys. Chem. Solids, 31 (1970) 39112. Jackson, T. J., et al., J. Phys.: Condens. Matter, 12 (2000) 1399