Application of Landau-Lifshitz-Bloch dynamics to grain switching in heat-assisted magnetic recording

Magnetization dynamics in heat-assisted magnetic recording (HAMR) involves magnetization collapse and re-formation under rapid local temperature excursion in a temporally varying applied magnetic field, with temperature likely moving above and below the medium Curie point on nanosecond timescales. Traditional micromagnetic simulation of the writing process in magnetic data storage has been restricted to isothermal processes in which macrospin magnetization dynamics are handled with the well-established Landau-Lifshitz-Gilbert (LLG) algorithm or close variants. Classical LLG treats the magnitude of material magnetization M as fixed (at zero Kelvin), so initial attempts at micromagnetic analysis of HAMR have typically dealt with the effects of temperature variation in HAMR in a somewhat ad hoc manner (e.g., insertion of M(T), A(T), K(T)), and have not been rigorous. A much improved treatment of this problem substitutes the Landau-Lifshitz-Bloch (LLB) algorithm in which thermally driven magnetization variation is treated more correctly in an extended semi-classical Landau-Lifshitz framework Here we study single-grain switching with this method under application of time-varying temperature and H-field. For a typical system setup, we map phase diagrams of grain switching probability over the space of important HAMR parameters such as peak temperature elevation, applied H-field strength, and the synchronization of temperature and field.