Fast vortex core switching at high temperatures

Abstract

Fast ferromagnetic vortex core switching is investigated employing micromagnetic simulations. Short pulse (in the range of a few hundreds of picoseconds) of an in-plane oscillating magnetic field is applied to a thin disk (diameter 200nm and thickness 20nm) with material parameters resembling permalloy. Fundamental frequency of this excitation field is close to the resonance with the material spin waves. Thermal effects are introduced by replacing the Landau–Lifshitz–Gilbert equation by the Landau–Lifshitz–Bloch equation. Temperature from 300K to 850K is considered, just below the Curie temperature TC=870K. Calculations are done within the oommf simulation framework.We find that: (i) Period of the field necessary to switch the vortex increases approximately from 141ps at 300K to 572ps for the high-temperature limit. (ii) Amplitude of the field necessary to switch the vortex core decreases roughly from 60mT to 15mT – even at high temperatures this amplitude is nonzero, contrary to the case of quasi-static switching. (iii) Time span between the excitation and switching (switching time) seems not to depend on the temperature. (iv) Duration of the switching itself (movement of the Bloch point in the sample) increases from a few picoseconds at low temperatures to tens of picoseconds at high temperatures.