Thermally Activated Magnetic Switching Mode for Various Thicknesses of Perpendicularly Ferromagnetic Nano-dot

Abstract

Even applying thermal pulse has been succeeded to reduce the coercivity through randomization the magnetization in such a way stimulate the magnetic reversion, the efficiency of magnetic switching field consumption in writing process still turns out to be an exciting research field to implement the HAMR technology. One of the remarkable geometric properties of HAMR storage media that can be correlated to the writing field reduction issue is the nano-dot thickness. Furthermore, thermal fluctuation causes the magnetization switching process to be probabilistic. This magnetic switching probability determines the magnitude of the writing field. This paper aims to investigate the impact of changes in media thickness on the magnetization process in particular at high temperatures numerically. Nano-dot was modeled as a parallelepiped with uniaxial anisotropy which was regarded as a magnetically isolated system where no disturbance field of neighboring nano-dots. Simulation arrangements were implemented to evaluate the two viewpoints in the current heat-assisted magnetic recording, either coercivity, as well as writing field consume. Coercivity was gauged by inducing a magnetic field which linearly increased up to 2 Tesla for 2.5 ns at thermal equilibrium to the surrounding. In evaluating writing field consume, thermal field pulse which just below the Curie temperature was generated while the magnetic field inducing the nano-dot. These schemes investigations were based on the Landau-Lifshift- Gilbert equation which accommodates the fluctuation-dissipation theorem in calculating thermal fluctuation effect. Also, temperature dependent material parameters such as magnetic saturation, magnetic anisotropy, and exchange interaction, were taken into account. At room temperature, the coercive and nucleation fields are highly sensitive to the nano-dot thickness. Under thermal assistance, the writing field for 10 nm and 100 nm of the chosen thicknesses are 0.110 T and 0.125 T respectively. These writing grades are significantly lower than the coercivity of the media. For both thicknesses, zero field magnetization reversal phenomena are observed as indicated by the existences of the switching probabilities at H = 0. This numerical study showed that using the heating assistance close to the Curie point, nanodots with the chosen thicknesses and magnetic parameters were probably to be magnetized even no driven magnetic field. Along with this result, magnetic field induction which required to utterly magnetizing was only in the sub-Tesla - about a tenth of the coercive field. During magnetization processes under thermal assistance, randomization of magnetic moments initiated the switching dynamic before the domain wall was nucleated and propagated to reach a single magnetized domain.