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Magnetic Nanoclusters

By: Adam Krause2/27/07

Physics 672

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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

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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

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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.

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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

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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

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Laser Vaporization

Figure above from: Billas et al., J. Magn. Magn. Mater. 168 (1997) 64

Metal Nanoclusters Produced By Laser Vaporization

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Stern-Gerlach Apparatus

Figure above from: Billas et al., J. Magn. Magn. Mater. 168 (1997) 64

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Description of magnetic particles

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Band Structure Evolution

Figure above from: Billas et al., J. Magn. Magn. Mater. 168 (1997) 64

Increasing Coordination Number

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Magnetic Moment vs. Cluster Size

Figure above from: Billas et al., J. Magn. Magn. Mater. 168 (1997) 64

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Closed Shell Cluster Size vs. Magnetic Moment Minima.

Table above from: Jensen, P. J., and K. H. Bennemann, Z. Phys. D. 35 (1995) 273

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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

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Magnetic Moment vs. Temperature

Fe

Ni

Co

Graphs from: Billas, M. L., A. Chatelain, and W. A. de Heer, Science 265 (1994) 1682

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Monte Carlo Simulation of Magnetization vs. 1/Temp

Graph from: Binder, K., et al., J. Phys. Chem. Solids, 31 (1970) 391

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Superparamagnetism

Magnetization Loops of Fe Nanoclusters

Graph from: Jackson, T. J., et al., J. Phys.: Condens. Matter, 12 (2000) 1399

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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.

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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