Nanoscale confinement of ultrafast spin transfer torque exciting non-uniform spin dynamics by femtosecond spin current pulses

TL;DR

This paper investigates how femtosecond spin current pulses can induce non-uniform, ultrafast spin dynamics in ferromagnets, revealing nanoscale confinement and high-frequency excitations relevant for advancing spintronics.

Contribution

It demonstrates the use of laser-generated ultrashort spin current pulses to excite and analyze localized, high-frequency spin dynamics at the nanometer scale.

Findings

Ultrashort spin current pulses induce inhomogeneous spin dynamics up to 0.6 THz.

Magnetization perturbation is confined within 2 nm.

The approach enables probing of non-uniform magnetization dynamics.

Abstract

Spintronics had a widespread impact over the past decades due to transferring information by spin rather than electric currents. Its further development requires miniaturization and reduction of characteristic timescales of spin dynamics combining the sub-nanometer spatial and femtosecond temporal ranges. These demands shift the focus of interest towards the fundamental open question of the interaction of femtosecond spin current (SC) pulses with a ferromagnet (FM). The spatio-temporal properties of the impulsive spin transfer torque exerted by ultrashort SC pulses on the FM open the time domain for probing non-uniform magnetization dynamics. Here we employ laser-generated ultrashort SC pulses for driving ultrafast spin dynamics in FM and analyzing its transient local source. Transverse spins injected into FM excite inhomogeneous high-frequency spin dynamics up to 0.6 THz, indicating that the perturbation of the FM magnetization is confined to 2 nm.