DIPOLE-EXCHANGE SPIN WAVES IN FERROMAGNETIC NANOSTRUCTURES WITH SPHERICAL GEOMETRIES

Hoa T. Nguyen and M. G. Cottam
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Hoa T. Nguyen: Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada N6A 3K7, Canada
M. G. Cottam: Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada N6A 3K7, Canada

Surface Review and Letters (SRL), 2008, vol. 15, issue 06, 727-744

Abstract: Dipole–exchange spin waves (SWs) are studied in ferromagnetic nanostructures with spherical geometries such as spheres, part spheres, and spherical shells, both individually and in finite-sized arrays. A microscopic theory is used based on a spin Hamiltonian, which incorporates the short-range exchange and long-range magnetic dipole–dipole interactions, as well as an external magnetic field applied in any direction. Our theory is advantageous for describing the dynamical properties of inhomogeneously magnetized samples, and the use of phenomenological boundary conditions is avoided. Numerical results are deduced for the frequencies of the discrete SW modes and their dependence on the radius, spacing between particles, applied field, etc. Applications are made to PermalloyFe19Ni81and alloyCo80Ni20nanoparticles with their sizes varying from 10 to 100 nm. Through a Green function theory, the spatial distributions and spectral intensities of the SWs are also deduced. The mode-mixing (hybridization) effects on the SW branches are found to be important, depending on the particle sizes and geometries.

Keywords: Spin waves; dipole-exchange models; ferromagnets; magnetic spheres; magnetic nanoparticles; 75.30.Ds; 75.40.Gb; 75.75.+a (search for similar items in EconPapers)
Date: 2008
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DOI: 10.1142/S0218625X08011949

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