Simulations of magnetic hysteresis loops for dual layer recording media

Abstract

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.

Phase-field-crystal model for magnetocrystalline interactions in isotropic ferromagnetic solids

“…The LLG approach and its many variants has been used to study domain walls, effect of disorder and it has been even connected to density functional theory computations [52][53][54], for a review see, e.g., Kurzik and Prohl [55]. In LLG, the dynamic equations are solved in a lattice but there is no direct connection with the underlaying atomic structure.…”

Simulations of magnetic hysteresis loops at high temperatures

“…It is based on the 0021-8979/2014/116(12)/123910/5/$30.00 V C 2014 AIP Publishing LLC 116, 123910-1 determination of the time between grain reversal calculated by the Arrhenius-Neel law, which assigns a switching probability to individual grain magnetic moments under the influence of local anisotropy, and an effective field from the other grain moments and the external field. 3,4 Our implementation of KMC uses LLG to relax the system to equilibrium after an individual grain moment is reversed. The Arrhenius-Neel expression for the mean reversal time involves the attempt frequency f 0 , which is both field and temperature dependent.…”

“…A constant value was thus adopted (a ¼ 0.05), as in our previous applications of KMC and LLG micromagnetic simulations. 3,4,9 As a prelude to the examination of the temperature dependence of MH loops, we show first a comparison of LLG and KMC at 600 K over a range of values of sweep rate R in Fig. 1.…”

“…This approach has the advantage that it can span much longer time scales than stochastic LLG while using the same microscopic parameters. [2][3][4] The KMC algorithm therefore complements the LLG method and it has been shown that in regimes where the two methods can be applied they give good agreement. 3 Evaluation of high anisotropy heat-assisted magnetic recording (HAMR) media 5-8 is of current interest.…”

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

“…21, this KMC algorithm was applied to study M H hysteresis loops of dual layer ECC recording media at finite temperature and long time scales in which the effect of ECC interlayer exchange coupling was treated in the same way as the intralayer exchange coupling by means of an effective field. ECC media for practical applications has a relatively strong exchange coupling and it is not evident that treating the intralayer coupling through an effective field is a good approximation 8 for this purpose as it ignores the correlated nature of the rotation of the layers in the reversal process.…”