Microwave-assisted magnetic recording at lower transverse oscillating field

Abstract

Microwave-assisted magnetization reversal is a promising approach to overcome thermal instabilities and to achieve high magnetic recording densities. In this work, micromagnetic simulations are conducted to investigate the influence of square resonance fields on magnetic recording. We observe that lower switching field can be achieved with square microwave fields as compared to sinusoidal transverse fields because it has a larger spectral energy and a wider Fourier spectra. The wide Fourier spectra also induce a second switching field minimal at a lower frequency, implying that assisted switching can potentially be achieved at around 1/3 of the frequency of pure sinusoidal resonance field. It is found that the presence of the third harmonic component is sufficient to produce similar magnetic behavior. This observation forms the design basis of our modified spin torque oscillator, which generates a transverse field containing a strong power spectrum density at the first and the third harmonics, for microwave-assisted recording. With the inherent tradeoff between field strength and frequency, the new oscillator has a distinct advantage because field strength is contributed mainly by the low frequency component.