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Computational Nanomagnets
M. McGuigan, J.W. Davenport, and J. Glimm
Nanomagnets are important materials for high-density data storage.
Storage densities of 1012 bits/in2 are possible while maintaining thermal
stability at room temperature [1]. To design such materials we have devised
and validated a computational approach that takes first principles
calculations from density functional theory as input to a quantum Heisenberg
model using a spin-wave or magnon description. We established the validity
of these methods through comparison to experimental data [2], see Figure 1.
We studied an iron nanoribbon of dimension 14 x 167 x 12700 atoms (4nm x
48nm x 3645nm) and with a total of 59,385,200 atoms. The comparison shows
that computations based on spin wave theory can accurately predict the
material properties of nanomagnets below 400K. Above that temperature magnon
interactions become important. These higher temperatures to the Curie point
can be treated by quantum Monte Carlo methods running on modern
supercomputers. The method we developed exceeds by many orders of magnitude
the feasible problem size of density functional calculations in terms of the
number of atoms treated. The extension of these methods to composite
materials is in progress.
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| Figure 1. Magnetization curve for an iron nanoribbon with 14
x 167 x12700 atoms (total of 59,385,200 atoms). Experimental
data from Crespo et al [3]. |
References
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[1] Haast, M. Pattern magnetic thin films for ultra high density
recording. Thesis, ISBN-90-3613456 (1999).
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[2] McGuigan, M., Davenport, J., and Glimm, J. Computational approach to
finite size and shape effects in iron nanomagnets. Preprint (Oct. 2006).
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[3] Crespo, P., Gonzalez, J., Hernando, A., and Yndurain, F. Spin-wave
excitations in ribbon-shaped Fe nanoparticles. Phys. Rev. B 69: 012403
(2004).
Last Modified: April 23, 2009
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