Heat-assisted magnetic recording (HAMR) technology represents the most promising candidate to replace the current perpendicular recording paradigm to achieve higher storage densities. To better understand HAMR dynamics in granular media we need to describe accurately the magnetization dynamics up to temperatures close to the Curie point. To this end we propose a multiscale approach based on the Landau-Lifshitz-Bloch (LLB) equation of motion parametrized using atomistic calculations. The LLB formalism describes the magnetization dynamics at finite temperature and allows us to efficiently simulate large system sizes and long time scales. Atomistic simulations provide the required temperature dependent input quantities for the LLB equation, such as the equilibrium magnetization and the anisotropy and can be used to capture the detailed magnetization dynamics. The multiscale approach makes it possible to overcome the computational limitations of atomistic models in dealing with large systems, such as a recording track, while incorporating the basic physics of the HAMR process. We investigate the magnetization dynamics of a single FePt grain as a function of the properties of the temperature profile and applied field and test the LLB results against atomistic calculations. Our results prove the appropriateness and potential of the approach proposed here where the granular model is able to reproduce the atomistic simulations and capture the main properties of a HAMR medium.

Granular magnetic recording media with perpendicular anisotropy are the basis of information storage in hard drive. This is the case for current media and future technologies such as heat assisted magnetic recording (HAMR), microwave assisted magnetic recording (MAMR) and heated dots. It is therefore important to understand the common methods of media characterisation, which often use quasi-static magnetic measurements. A granular micromagnetic model based on the kinetic Monte Carlo (kMC) approach is developed to investigate the timescales relevant to these measurements. The model is used to investigate the effects of the microstructure and the intergranular interactions on the magnetic properties including the angular dependence of the magnetisation and the time dependence of the coercivity. The latter is shown to be strongly dependent on intergranular interactions.

An exchange bias (EB) model taking the setting process into account is developed to study the effect of the crucial parameters, such as the AFM anisotropy constant ([Formula: see text]), the setting temperature ([Formula: see text]), and the physical microstructure on the exchange bias field of an AFM/FM system. The magnetization dynamics of the EB system is treated using the kinetic Monte Carlo approach and by integrating the Landau–Lifshitz–Gilbert equation for AFM and FM layers, respectively. We first investigate the variation of the exchange bias field ([Formula: see text]) as a function of [Formula: see text] in the IrMn/CoFe system. It is found that [Formula: see text] strongly depends on the energy barrier dispersion determined by dispersions of [Formula: see text] and the grain volume. It is shown that the [Formula: see text] is affected by the physical microstructure of the IrMn layer: film thickness and grain diameter. We also demonstrate that the maximum setting fraction ([Formula: see text]) related to [Formula: see text] can be achieved by optimizing the value of [Formula: see text] and [Formula: see text]. The simulation results of the setting process are in good agreement with previous experimental works. This confirms the validity of the EB model, including the setting process that can be used as a powerful tool for the application of spintronics, especially for read sensor design to achieve high thermal stability with scaling down of components.

A micromagnetic model of an exchange bias bilayer is used to examine the impact of the physical structure and the easy axis dispersion of the antiferromagnetic (AF) layer on the exchange bias field (H EB) in an IrMn/CoFe system. Because of the different timescales, the magnetization dynamics of the IrMn and CoFe layers are modelled using respectively a kinetic Monte Carlo (kMC) approach and Landau-Lifshitz-Gilbert (LLG) equation. The easy axis dispersion is modelled using a Gaussian distribution. The calculations show that H EB increases with increasing IrMn thickness and grain size, in agreement with experimental work. Moreover, the model allows the visualization of the switching process at the micromagnetic level to reveal the reversal mechanism. We find that the effect of AF easy axis distribution not only strongly affects the reduction of H EB but also drives non-coherent behaviour in the reversal mechanism. This confirms that the easy axis distribution is an important factor with strong impact on the magnetic properties and exchange bias field of an exchange bias system.