Exchange scaling of ultrafast angular momentum transfer in 4$\it{f}$ antiferromagnets

TL;DR

This study explores how the RKKY interaction influences ultrafast angular momentum transfer in 4f antiferromagnets, revealing that transfer rates depend on RKKY magnitude, which can be tuned via 4f electron occupation.

Contribution

It demonstrates the direct link between RKKY strength and ultrafast spin transfer rates in 4f antiferromagnets, combining experimental and theoretical methods.

Findings

Transfer rate is proportional to RKKY magnitude.

Systematic variation of 4f occupation alters RKKY and transfer speed.

Potential for tuning magnetic device speeds via conduction electron manipulation.

Abstract

Ultrafast manipulation of the magnetic state of matter bears great potential for future information technologies. While demagnetisation in ferromagnets is governed by dissipation of angular momentum, materials with multiple spin sublattices, e.g. antiferromagnets, can allow direct angular momentum transfer between opposing spins, promising faster functionality. In lanthanides, 4$\it{f}$ magnetic exchange is mediated indirectly through the conduction electrons (the Ruderman-Kittel-Kasuya-Yosida interaction, RKKY), and the effect of such conditions on direct spin transfer processes is largely unexplored. Here, we investigate ultrafast magnetization dynamics in 4f antiferromagnets, and systematically vary the 4$\it{f}$ occupation, thereby altering the magnitude of RKKY. By combining time-resolved soft x-ray diffraction with ab-initio calculations, we find that the rate of direct transfer between opposing moments is directly determined by the magnitude of RKKY. Given the high sensitivity of RKKY to the conduction electrons, our results offer a novel approach for fine-tuning the speed of magnetic devices.