Magnetization dynamics with a spin-transfer torque

TL;DR

This paper investigates the magnetization dynamics in a nanoscale spin valve using micromagnetic simulations, revealing complex behaviors like multiple hysteresis features, precessional states, and unique thermal activation effects driven by spin-transfer torque.

Contribution

It provides new insights into the steady-state and pulsed current effects on magnetization reversal and dynamics, highlighting the complex interplay of spin torque, damping, and energy oscillations.

Findings

Multiple jumps and plateaus in hysteresis loops

Quantitative criteria for magnetization reversal with pulsed current

Distinct thermal activation behavior due to spin torque

Abstract

The magnetization reversal and dynamics of a spin valve pillar, whose lateral size is 64$\times$64 nm$^2$, are studied by using micromagnetic simulation in the presence of spin transfer torque. Spin torques display both characteristics of magnetic damping (or anti-damping) and of an effective magnetic field. For a steady-state current, both M-I and M-H hysteresis loops show unique features, including multiple jumps, unusual plateaus and precessional states. These states originate from the competition between the energy dissipation due to Gilbert damping and the energy accumulation due to the spin torque supplied by the spin current. The magnetic energy oscillates as a function of time even for a steady-state current. For a pulsed current, the minimum width and amplitude of the spin torque for achieving current-driven magnetization reversal are quantitatively determined. The spin torque also shows very interesting thermal activation that is fundamentally different from an ordinary damping effect.