Kinetic Monte Carlo approach to modeling thermal decay in perpendicular recording media

Abstract

A procedure is developed to study the evolution of high anisotropy magnetic recording media due to thermally activated grain reversal. It is assumed that the system is composed of single domain grains that evolves by passing through a sequence of relatively long-lived metastable states punctuated by abrupt reversals of individual grains. Solutions to the rate equations describing the sequence of metastable states are calculated using kinetic Monte Carlo. Transition rates are formulated from the Arrhenius-Néel expression in terms of the material parameters, temperature, and applied field. Results obtained from this method are shown to be in good agreement with those calculated from finite-temperature micromagnetics. The method is applied to study the rate dependence of finite-temperature MH loops and the thermal degradation of a recorded bit pattern in perpendicular recording media. A significant advantage of the procedure is its ability to extend simulations over time intervals many orders of magnitude greater than is feasible using standard finite-temperature micromagnetics with relatively modest computational effort.

Micromagnetic modeling of experimental hysteresis loops for heterogeneous electrodeposited cobalt films

“…24 Standard LLG simulations at experimental time scales (R $ 10 À8 Oe=ns) have impractically long run times; however, a semi-analytic model for this purpose has recently been developed which combines an energy barrier calculation along with thermal Monte Carlo simulations. 25 Fig. 2(b) shows representative results and the corresponding experimental data for an in-plane applied field.…”

“…Simulations on related magnetic thin-film systems suggest that this scaling holds, even at long time scales, in cases of weak inter-particle interactions. 6,25 Extrapolation to experimental times scales (R ¼ 10 À8 Oe=ns) has a large associated error, yielding H c ¼ 1906100 Oe for the in-plane loops and H c ¼ 1206100 Oe for the out-of-plane loops. Nevertheless, these values are consistent with the experimental result that H c ¼ 150610 Oe for both field orientations for uniform films at 300 K.…”

Micromagnetic simulations of sweep-rate dependent coercivity in perpendicular recording media

“…A more reliable means by which to use long-time experimental room-temperature M-H media loops as means by which to fit short-time microscopic modeling parameters would be valuable for use in recording models. 18 Full characterization requires agreement between the modeled results and experimental loops for the field applied in any direction. Simulations of the longer-term decay of recorded media transitions is even more of an issue.…”

“…This reduces H 0 by factors of 0.86 and 0.50 in the cases of φ=0 0 and 45 0 , respectively. 18 Next, we adopt the formulation of Wood 17 to set the value of the exponent n where an approximate formula is given (for a single SW grain) as a function of φ, which we have also extended to account for the angular. 18 When this is done, we find n=1.78 for φ=0 0 and n=1.42 for φ=45 0 .…”

Thermally activated switching at long time scales in exchange-coupled magnetic grains

“…[12][13][14][15][16] In Ref. 17, a KMC algorithm to study long-time scale thermally activated grain reversal of single layer recording media was described. The Arrhenius-Néel expression for the rate coefficients between the minimum energy states of the individual grains was used to calculate the time between successive reversals.…”