It is common to model recording media as interacting coherently rotating magnetic moments, but real materials frequently exhibit perpendicular switching fields less than the anisotropy field and a different angular dependence than theoretically expected. Micromagnetic simulations were performed, which included multiple elements per grain and magnetostatic interactions between elements. Two likely explanations have emerged from this analysis: the existence of low anisotropy regions within the first few atomic layers of the sputtered film or anisotropy gradation throughout the grain thickness. Both explanations offer appropriate coercivity reductions; however, grains including anisotropy gradation display this effect at more realistic values of intragranular exchange. A simplified two element model was fit to the multidomain angle-dependent results in order to find a computationally simple description that can be easily included in a recording simulation.
Bibliographical noteFunding Information:
We thank A. Yu. Dobin for numerous useful discussions and exposure to experimental data. Funding was provided by Seagate Technologies, the IGERT Program of the National Science Foundation under Award No. DGE-20114372 and the National Science Foundation REU Program under Award No. EEC-0648954.