Time domain detection of pulsed spin torque damping reduction

TL;DR

This paper demonstrates time-domain detection of spin torque damping reduction using ultrafast pulses, revealing transient precession behaviors and conditions for damping cancellation.

Contribution

It introduces a method for observing transient spin dynamics with ultrafast pulses and identifies the pulse characteristics needed for damping cancellation.

Findings

Transient precession evolves from 1 ns to stable oscillations over 2 ns.

Short, fast-rise pulses are essential for complete damping cancellation.

Transient trajectories relax to a nearly zero damping stable orbit.

Abstract

Combining multiple ultrafast spin torque impulses with a 5 nanosecond duration pulse for damping reduction, we observe time-domain precession which evolves from an initial 1 ns duration transient with changing precessional amplitude to constant amplitude oscillations persisting for over 2 ns. These results are consistent with relaxation of the transient trajectories to a stable orbit with nearly zero damping. We find that in order to observe complete damping cancellation and the transient behavior in a time domain sampling measurement, a short duration, fast rise-time pulse is required to cancel damping without significant trajectory dephasing.