Hysteresis Loops of Recording Media Grains Under the Influence of High-Frequency Fields

Hysteresis loops of single grains and recording media were calculated under the influence of high-frequency (HF) magnetic fields, similar to those produced by a spin-torque oscillator (STO) in microwave-assisted magnetic recording (MAMR). The effect of the HF field ellipticity and the strength of magnetostatic interactions between grains were investigated. Elliptical HF fields with a major:minor axis ratio of 6:1 were almost as effective as circular HF fields in reducing the media coercivity. For media with a small grain pitch, i.e., strong magnetostatic interactions between grains, the HF field was able to reduce the coercivity by much more than when the grains were far apart, and magnetostatic interactions were weak.