Thermally assisted magnetization reversal of a magnetic nanoparticle driven by a down-chirp microwave field pulse

Abstract

Fast magnetization reversal of a single-domain magnetic nanoparticle can be achieved by a linear down-chirp microwave field pulse (DCMWP) in zero temperature limit. Certain requirements for the microwave wave amplitude, chirp rate, and initial frequency have to be satisfied for the reversal. However, the generation of such DCMWP in practice is a challenging issue, and the finite temperature is ubiquitous in practice. Here, we study the effect of finite temperature on DCMWP-induced magnetization reversal based on the stochastic Landau-Lifshitz-Gilbert equation. It is found that the DCMWP with significantly smaller amplitude, chirp rates, and initial frequency induces fast and more energy efficient magnetization reversal. The critical temperature, which is defined as the maximal temperature at which fast and energy-efficient reversal is valid, increases with enlarging the system size and hence a wide operating temperature above room temperature is possible in reality. It is because the energy barrier/thermal stability increases with the volume of the system, but the effective magnetization decreases with temperature, which induces faster magnetization reversal. These findings may provide a way to realize low-cost and fast magnetization reversal with a wide operating temperature.