Spin current driven by ultrafast magnetization of FeRh

TL;DR

This study investigates how ultrafast laser-induced magnetization in FeRh generates a spin current, revealing the transfer of angular momentum from electrons to magnons and phonons, and providing insights into angular momentum dynamics in magnetic materials.

Contribution

First direct measurement of spin current driven by ultrafast magnetization in FeRh, clarifying angular momentum transfer mechanisms in this process.

Findings

Strong correlation between spin current and magnetization change rate.

Angular momentum transfer from electron bath to magnon bath is confirmed.

Spin current is involved in the build-up of magnetization, not just dissipation.

Abstract

Laser-induced ultrafast demagnetization is an important phenomenon that probes arguably ultimate limits of the angular momentum dynamics in solid. Unfortunately, many aspects of the dynamics remain unclear except that the demagnetization transfers the angular momentum eventually to the lattice. In particular, roles of electron-carried spin current are debated. Here we experimentally probe the spin current in the opposite phenomenon, i.e., laser-induced ultrafast magnetization of FeRh, where the laser pump pulse initiates the angular momentum build-up rather than its dissipation. Using the time-resolved magneto-optical Kerr effect, we directly measure the ultrafast-magnetization-driven spin current in a FeRh/Cu heterostructure. Strong correlation between the spin current and the net magnetization change rate of FeRh is found even though the spin filter effect is negligible in this opposite process. This result implies that the angular momentum build-up is achieved by an angular momentum transfer from the electron bath (supplier) to the magnon bath (receiver) and followed by the spatial transport of angular momentum (spin current) and dissipation of angular momentum to the phonon bath (spin relaxation).