Magnetic viscosity in high-density recording

Abstract

For future ultrahigh-density magnetic recording, the magnetic viscosity in thin-film media will become an issue due to the drastic reduction in grain size. An algorithm combining a Monte Carlo method and molecular dynamics was employed to study the thermal effects in thin-film media. The component of the field perpendicular to the plane defined by the axes of shape anisotropy and uniaxial crystalline anisotropy makes it necessary to use the three-dimensional energy surface to find the minimum energy barrier. This barrier is used to sample the reversal rate and the elapsed time. Hysteresis loops for various KuV/kT ratios and sweep times are simulated. Isolated and di-bit transitions are written, taking into account thermally assisted switching. After the head field is turned off, the subsequent thermal decay is computed for time spans as long as 6 months. Significant aftereffect is found for grain volumes about twice that for ordinary superparamagnetism.

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

“…A similarly poor fit was determined in the case of ECC media. For the field applied normal to the plane, the resulting f 0 values again were unphysical, ranging from 6.3 x10 6 GHz to 58 GHz. Fig.…”

“…For ECC media the above parameters were used for the hard layer. A second thinner soft layer using 8x8x5 nm 3 grains was added to the simulation with M s2 =600 emu/cc, weaker (perpendicular) anisotropy K 2 =1.5x10 6 erg/cc and inter-grain exchange again set at A 2 =0.05 µerg/cm (although it can be larger for some real media). Gaussian distributions as in the hard layer were also assumed.…”

“…[3][4][5] Several other approaches include early work that combines an LLG calculation of the energy barriers with Monte Carlo (MC) simulations of the switching probability which allows for a completely numerical prediction of the long-time coercive force. 6 More recently, MC or LLG simulations have been combined with nudged elastic band model to estimate these effects on single particles or grains of interacting exchange spring bi-layers, with fields applied in various directions. 7,8 An alternative scheme has also been proposed which is based on Arrhenius-Néel scaling of short-time hightemperature, LLG simulations of M-H loops to estimate longtime room-temperature switching behavior.…”

Morphological Change in FePt Nanogranular Thin Films Induced by Irradiation with 2.4 MeV Cu<SUP>2+</SUP> Ions: Electron Tomography Observation

“…1) However, the magnetic recording becomes unstable by thermal fluctuation if the size of magnetic grains gets smaller than a critical value. 2,3) The critical size to superparamagnetism is generally reduced with enhancement of magnetic anisotropy. It is required to develop materials with high magnetic anisotropy to overcome the problem.…”

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

“…11 For the purpose of studying long-time scale micromagnetics governed by thermally activated processes, Kinetic Monte Carlo (KMC) methods have proven useful. [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.…”