J. I. Mercer

Simulations of magnetic hysteresis loops for dual layer recording media

A Kinetic Monte-Carlo algorithm is applied to examine MH loops of dual-layer magnetic recording media at finite temperature and long time scales associated with typical experimental measurements. In contrast with standard micromagnetic simulations, which are limited to the ns-μs time regime, our approach allows for the direct calculation of magnetic configurations over periods from minutes to years. The model is used to fit anisotropy and coupling parameters to experimental data on exchange-coupled composite media which are shown to deviate significantly from standard micromagnetic results. Sensitivities of the loops to anisotropy, inter-layer exchange coupling, temperature, and sweep rate are examined.

Kinetic Monte Carlo Simulations of

Our previously developed kinetic Monte Carlo algorithm is used to simulate M-H loops of high anisotropy magnetic recording media at long time scales relevant to the experimental measurements using the magneto-optic Kerr effect. Micromagnetic parameters are fit to loop data taken at 300 K and at a sweep rate of 700 Oe/s on a single-layer media developed for heat-assisted magnetic recording. Significantly different fitted parameters result from standard micromagnetic simulations that can access only sweep rates many orders of magnitude faster. Sensitivities of the loops to anisotropy, saturation magnetization, and various distributions are reported.

M\!\!-\!\!H

Micromagnetic modeling provides a realistic description of the magnetic switching behavior in electrodeposited Co thin films that are either uniform (untemplated) or templated with an array of sub-micron spheres. Quantitative agreement between experimental results and simulations based on the Landau-Lifshitz-Gilbert equations is achieved for both in-plane and perpendicular MH loops at two temperatures. By accounting for the sweep-rate dependence in coercivity values from simulated loops (with sweep rates 104–10−1 Oe/ns) and then extrapolating to the experimental regime (measurement times of 10–100 s), a self-consistent set of microscopic parameters is established to accommodate the complexity of the electrodeposited films.

Loops for HAMR Recording Media: Comparison With MOKE Data

A series of atomistic finite temperature simulations on a model of an FCC lattice of maghemite nanoparticles using the stochastic Landau-Lifshitz-Gilbert (sLLG) equation are presented. The model exhibits a ferromagnetic transition that is in good agreement with theoretical expectations. The simulations also reveal an orientational disorder in the orientational order parameter for

Micromagnetic modeling of experimental hysteresis loops for heterogeneous electrodeposited cobalt films

T < 0.5 T_c

Dipolar ferromagnetism in three-dimensional superlattices of nanoparticles

due to pinning of the surface domain walls of the nanoparticles by surface vacancies. The extent of the competition between surface pinning and dipolar interactions provides support for the conjecture that recent measurements on systems of FCC superlattices of iron-oxide nanoparticles provide evidence for dipolar ferromagnetism is discussed.