Origin of the laser-induced picosecond spin current across magnetization compensation in ferrimagnetic GdCo

TL;DR

This study explores laser-induced ultrafast spin currents in GdCo ferrimagnet, revealing how magnetic domain formation and sublattice contributions influence terahertz emission at magnetization compensation points.

Contribution

It demonstrates the role of magnetic domains and sublattice dynamics in spin current generation across magnetization compensation in GdCo.

Findings

THz emission is suppressed at magnetization compensation with magnetic field.

Spin current persists at compensation without an external magnetic field.

Spectral blueshift indicates magnetic domain formation near compensation.

Abstract

The optical manipulation of magnetism enabled by rare earth-transition metal ferrimagnets holds the promise of ultrafast, energy efficient spintronic technologies. This work investigates laser-induced picosecond spin currents generated by ferrimagnetic GdCo via terahertz emission spectroscopy. A suppression of the THz emission and spin current is observed at magnetization compensation when varying the temperature or alloy composition in the presence of a magnetic field. It is demonstrated that this is due to the formation of domains in the GdCo equilibrium magnetic configuration. Without an applied magnetic field, the picosecond spin current persists at the compensation point. The experimental findings support the model for THz spin current generation based on transport of hot spin-polarized electrons, which is dominated by the Co sublattice at room temperature. Only at low temperature a comparable contribution from Gd is detected but with slower dynamics. Finally, spectral analysis reveals a blueshift of the THz emission related to the formation of magnetic domains close to magnetization compensation.