Verification of ultrafast spin transfer effects in FeNi alloys

TL;DR

This study critically examines the optical intersite spin transfer effect in FeNi alloys, demonstrating that magneto-optical signal increases alone do not confirm spin transfer, and provides methods to reliably identify such effects.

Contribution

The paper introduces an extended data analysis approach that unambiguously detects spin transfer effects in FeNi alloys, clarifying previous ambiguities and the origin of delayed Ni demagnetization.

Findings

Magneto-optical signal increase alone is insufficient to confirm OISTR.

Extended data analysis can reliably identify spin transfer effects.

Resolved the debate on delayed Ni demagnetization in FeNi alloys.

Abstract

The optical intersite spin transfer (OISTR) effect was recently verified in Fe$_{50}$Ni$_{50}$ using magneto-optical Kerr measurements in the extreme ultraviolet range. However, one of the main experimental signatures analyzed in this work, namely a magnetic moment increase at a specific energy in Ni, was subsequently found also in pure Ni, where no transfer from one element to another is possible. Hence, it is a much-discussed issue whether OISTR in FeNi alloys is real and whether it can be verified experimentally or not. Here, we present a comparative study of spin transfer in Fe$_{50}$Ni$_{50}$, Fe$_{19}$Ni$_{81}$ and pure Ni. We conclusively show that an increase in the magneto-optical signal is indeed insufficient to verify OISTR. However, we also show how an extended data analysis overcomes this problem and allows to unambiguously identify spin transfer effects. Concomitantly, our work solves the long-standing riddle about the origin of delayed demagnetization behavior of Ni in FeNi alloys.