Time-Resolved Magnetic Relaxation of a Nanomagnet on Subnanosecond Time Scales

TL;DR

This paper introduces a two-pulse correlation method to measure subnanosecond magnetic relaxation times in nanomagnets, revealing a symmetry between excitation and relaxation and indicating more coherent dynamics in short time regimes.

Contribution

It presents a novel experimental approach for directly measuring magnetic relaxation times at subnanosecond scales in nanomagnets, supported by a macrospin model.

Findings

Two-pulse experiments match single-pulse switching probabilities based on delay.

Demonstrates symmetry between magnetic excitation and relaxation.

Finds more coherent magnetization dynamics in short time nonequilibrium regimes.

Abstract

We present a two-current-pulse temporal correlation experiment to study the intrinsic subnanosecond nonequilibrium magnetic dynamics of a nanomagnet during and following a pulse excitation. This method is applied to a model spin-transfer system, a spin valve nanopillar with perpendicular magnetic anisotropy. Two-pulses separated by a short delay (< 500 ps) are shown to lead to the same switching probability as a single pulse with a duration that depends on the delay. This demonstrates a remarkable symmetry between magnetic excitation and relaxation and provides a direct measurement of the magnetic relaxation time. The results are consistent with a simple finite temperature Fokker-Planck macrospin model of the dynamics, suggesting more coherent magnetization dynamics in this short time nonequilibrium limit than near equilibrium.