Spin treacle in a frustrated magnet observed with spin current

TL;DR

This study demonstrates the existence of a 'spin treacle' regime in frustrated nanometer-scale spin glasses, characterized by unique spin transport properties and magnetic fluctuation dynamics, verified through spin current measurements.

Contribution

It provides the first quantitative evidence of the 'spin treacle' regime in frustrated magnets using spin transport measurements and identifies its relation to spin freezing temperature.

Findings

Spin Hall angle remains temperature-independent at high temperatures.

The spin Hall angle decreases and vanishes at the spin freezing temperature.

The fluctuation time scale of local moments in the spin treacle is quantified.

Abstract

By means of spin current, the flow of spin angular momentum, we find a regime of "spin treacle" in a frustrated magnetic system. To establish its existence, we have performed spin transport measurements in nanometer-scale spin glasses. At temperatures high enough that the magnetic moments fluctuate at high frequencies, the spin Hall angle, the conversion yield between spin current and charge current, is independent of temperature. The spin Hall angle starts to decrease at a certain temperature $T^{*}$ and completely vanishes at a lower temperature. We argue that the latter corresponds to the spin freezing temperature $T_{\rm f}$ of the nanometer-scale spin glass, where the direction of conduction electron spin is randomized by the exchange coupling with the localized moments. The present experiment \textit{quantitatively} verifies the existence of a distinct "spin treacle" between $T_{\rm f}$ and $T^{*}$. We have also quantified a time scale of fluctuation of local magnetic moments in the spin treacle from the spin relaxation time of conduction electrons.