Effect of interlayer exchange coupling in spin-torque nano oscillator

TL;DR

This paper theoretically investigates how interlayer exchange coupling affects magnetization dynamics in spin-torque nano oscillators, revealing tunable high-frequency oscillations up to 300 GHz.

Contribution

It provides a theoretical analysis of interlayer exchange effects on STNO dynamics, deriving critical currents and demonstrating frequency tuning up to 300 GHz.

Findings

Magnetization states switch or oscillate due to coupling strengths.

Critical currents for oscillation are derived.

Oscillation frequency can reach 300 GHz.

Abstract

The dynamics of the magnetization of the free layer in a spin-torque nano oscillator (STNO) influenced by a noncollinear alignment between the magnetizations of the free and pinned layers due to an interlayer exchange coupling has been investigated theoretically. The orientations of the magnetization of the free layer with that of the pinned layer have been computed through the macrospin model and they are found to match well with experimental results. The bilinear and biquadratic coupling strengths make the current to switch the magnetization between two states or oscillate steadily. The expressions for the critical currents between which oscillations are possible and the critical bilinear coupling strength below which oscillations are not possible are derived. The frequency of the oscillations is shown to be tuned and increased to or above 300 GHz by the current which is the largest to date among nanopillar-shaped STNOs.