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Magnetic Nanoclusters

Magnetic Nanoclusters. By: Adam Krause 2/27/07 Physics 672. Nanocluster Quick Introduction. From a few atoms to several thousand atoms High fraction of atoms on the surface Different elements form different bonds and different nanocluster structures. A Few Types of Nanoclusters.

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Magnetic Nanoclusters

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  1. Magnetic Nanoclusters By: Adam Krause 2/27/07 Physics 672

  2. Nanocluster Quick Introduction • From a few atoms to several thousand atoms • High fraction of atoms on the surface • Different elements form different bonds and different nanocluster structures

  3. A Few Types of Nanoclusters Van der Waals Nanoclusters • Binding energy: < 0.3 eV / atom • Balance between induced dipole force and quantum closed shell interaction • Noble gases form icosahedral Van der Waals clusters Figure above from: Alonso, J. A., Structure and Properties of Atomic Nanoclusters, 2005

  4. A Few Types of Nanoclusters Van der Waals Nanoclusters • The drops at 148 and 309 atoms correspond to completed icosahedra. Figure above from: Echt, O., et al., J. Chem. Soc. Faraday Trans., 86 (1990) 2411

  5. A Few Types of Nanoclusters Ionic Nanoclusters • Bond Strength: 2-4 eV / atom • Tend to form boxes NaCl Cluster Graph above from: Martin, T. P., Physics Reports, 273 (1996) 199

  6. 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 A Few Types of Nanoclusters Metal Nanoclusters

  7. Laser Vaporization Metal Nanoclusters Produced By Laser Vaporization Figure above from: Billas et al., J. Magn. Magn. Mater. 168 (1997) 64

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

  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 (1) (2) Graphs from: Jensen, P. J., and K. H. Bennemann, Z. Phys. D. 35 (1995) 273

  14. Magnetic Moment vs. Temperature Co Ni Fe 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. References • Alonso, J. A., Structure and Properties of Atomic Nanoclusters (Imperial College Press, London, 2005). • Echt, O., et al., J. Chem. Soc. Faraday Trans., 86 (1990) 2411 • Martin, T. P., Physics Reports, 273 (1996) 199 • Dietz, T. G., et al., J. Chem. Phys., 74 (1981) 6511 • Bondybey, V. E., and J. H. English, J. Chem. Phys., 76 (1982) 2165 • Billas, M. L., A. Chatelain, and W. A. de Heer, J. Magn. Magn. Mater. 168 (1997) 64 • Cox, D. M., et al, Phys. Rev. B., 32 (1985) 7291 • Billas, M. L., A. Chatelain, and W. A. de Heer, Science 265 (1994) 1682 • Jensen, P. J., and K. H. Bennemann, Z. Phys. D. 35 (1995) 273 • Billas, M. L., et al., Phys. Rev. Lett., 71 (1993) 4067 • Binder, K., et al., J. Phys. Chem. Solids, 31 (1970) 391 • Jackson, T. J., et al., J. Phys.: Condens. Matter, 12 (2000) 1399

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