Spin torque oscillator for microwave assisted magnetization reversal

TL;DR

This theoretical study analyzes the conditions under which spin torque oscillators can generate self-oscillations suitable for microwave assisted magnetization reversal, highlighting the impact of magnetic field strength and material damping.

Contribution

It provides analytical formulas for critical currents and identifies the limitations on magnetic field and damping for effective MAMR applications.

Findings

Self-oscillation disappears above a critical magnetic field.

Materials with low damping are less suitable for wide-range self-oscillation.

Critical current formulas depend on material and field parameters.

Abstract

A theoretical study is given for the self-oscillation excited in a spin torque oscillator (STO) consisting of an in-plane magnetized free layer and a perpendicularly magnetized pinned layer in the presence of a perpendicular magnetic field. This type of STO is a potential candidate for a microwave source of microwave assisted magnetization reversal (MAMR). It is, however, found that the self-oscillation applicable to MAMR disappears when the perpendicular field is larger than a critical value, which is much smaller than a demagnetization field. This result provides a condition that the reversal field of a magnetic recording bit by MAMR in nanopillar structure should be smaller than the critical value. The analytical formulas of currents determining the critical field are obtained, which indicate that a material with a small damping is not preferable to acheive a wide range of the self-oscillation applicable to MAMR, although such a material is preferable from the view point of the reduction of the power consumption.