Regensburg 2004 – wissenschaftliches Programm
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MA: Magnetismus
MA 28: Spindynamik / Ummagnetisierungsvorg
änge
MA 28.2: Vortrag
Donnerstag, 11. März 2004, 15:30–15:45, H23
Atomic-scale model of thermal effects on magnetic anisotropy and dynamic switching properties of FePt nano-particles — •Ulrich Nowak1,2, Oleg Mryasov1, Konstantin Guslienko1, and Roy Chantrell1 — 1Seagate Research, 1251 Waterfront Place, Pittsburgh, PA, 15222, USA — 2Institut für Physik, Universität Duisburg-Essen, Germany
We propose a microscopic atomic-scale model of magnetic interactions in ordered L10 FePt based on an effective, classical spin Hamiltonian which is constructed with the use of first-principles calculations for non-collinear magnetic configurations and site-resolved magneto-crystalline anisotropy energies. Our effective Hamiltonian contains, in addition to the isotropic exchange, an effective, anisotropic exchange due to the strong single-ion anisotropy of the Pt atoms.
This model is studied numerically using Monte-Carlo methods as well as Langevin dynamics. The model allows to describe correctly the observed temperature dependence of the magnetic anisotropy energy of ordered FePt films. In particular the dependence of the anisotropy constant K1(T) on the reduced magnetization is found to be in excellent agreement with experimental results. Furthermore, the model is used to study the thermally induced switching behavior of FePt nano-particles. We find a strong deviation from the Neel-Brown theory for mean switching times due to the temperature dependence of the activation energy barrier.