Atomic level micromagnetic model of recording media switching at elevated temperatures

Abstract

An atomic level micromagnetic model of granular recording media is developed and applied to examine external field-induced grain switching at elevated temperatures which captures non-uniform reversal modes. The results are compared with traditional methods which employ the Landau-Lifshitz-Gilbert equations based on uniformly magnetized grains with assigned intrinsic temperature profiles for M (T ) and K(T ). Using nominal parameters corresponding to high-anisotropy FePt-type media envisioned for Energy Assisted Magnetic Recording, our results demonstrate that atomic-level reversal slightly reduces the field required to switch grains at elevated temperatures, but results in larger fluctuations, when compared to a uniformly magnetized grain model.

Monte Carlo simulations of intragrain spin effects in a quasi-2D Heisenberg model with uniaxial anisotropy

“…However, the present work suggests that even for room temperature modeling of materials such as Fe-Pt with T ′ c ≃ 800K, [15] the macrospin approximation is questionable and is certainly not appropriate when the material is heated close to T ′ c , as in the HAMR process, even with the temperature dependence of the magnetic moment of the grains included. To properly account for the impact of internal spin degrees of freedom on switching behavior of grain magnetization vectors under the influence of an applied magnetic field and thermal fluctuations requires the application of the more sophisticated atomistic calculations [3] or the Landau Lifshitz Bloch formalism [23]. Such methods include a more complete account of the internal spin degrees of freedom on both the static and dynamic properties of these high anisotropy materials.…”

“…The necessity for models of magnetic recording media that go beyond approximations based on the physics at the nanometer length scale is becoming increasingly important not only due to shrinking bit dimensions but also for the evaluation of new paradigms such as heat assisted magnetic recording (HAMR) [1,2]. The role of degrees of freedom internal to media grains, normally assumed to have uniform magnetization (referred to as the macrospin model), has been shown to be significant in field-induced reversal at temperatures which are comparable to the intrinsic ferromagnetic Curie point [3,4]. It is at temperatures near T c that HAMR technology operates.…”

Simulations of magnetic hysteresis loops at high temperatures

“…The simulation techniques used in this work have omitted effects due to thermally induced fluctuations in the magnitude of the grain moments as have been modeled previously through an atomistic approach 7,[17][18][19] or via the Landau-Lifshitz-Bloch (LLB) equations. 20,21 At the slower KMC time scales, it is unlikely the higher-energy fast dynamics associated with the strong inter-atomic exchange interactions will be important.…”

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

“…3 More recently, exchange coupled composite (ECC) media, composed of layers with varying anisotropy strengths, have brought further advances in making bits smaller and stable with acceptable SNR. 4 Further technical refinements of these recent paradigms will continue to bring incremental improvements but new technologies are being actively pursued, such as heat assisted magnetic recording [5][6][7] and bit patterned media. 8 In addition to significant advances in materials science and fabrication techniques, numerical modeling of the recording process has played a crucial role in the realization of areal density increases in recent decades 9 and continues to be a key part of the evaluation of new technologies.…”