Uncovering the Timescales of Spin Reorientation in $TbMn_{6}Sn_{6}$

TL;DR

This study measures the ultrafast timescale of spin reorientation in $TbMn_{6}Sn_{6}$, revealing it occurs within 12-24 ps and can be optically controlled, with implications for spintronics and data storage.

Contribution

First direct measurement of the spin reorientation timescale in $TbMn_{6}Sn_{6}$ using TMOKE, linking ultrafast dynamics to anisotropy-driven mechanisms.

Findings

Reorientation timescale spans 12-24 ps depending on excitation fluence.

Spin reorientation driven by large anisotropy energies on meV scales.

Model predicts possible 180° reorientation enabling optical control.

Abstract

$TbMn_{6}Sn_{6}$ is a ferrimagnetic material which exhibits a highly unusual phase transition near room temperature where spins remain collinear while the total magnetic moment rotates from out-of-plane to in-plane. The mechanisms underlying this phenomenon have been studied in the quasi-static limit and the reorientation has been attributed to the competing anisotropies of Tb and Mn, whose magnetic moments have very different temperature dependencies. In this work, we present the first measurement of the spin-reorientation transition in $TbMn_{6}Sn_{6}$. By probing very small signals with the transverse magneto-optical Kerr effect (TMOKE) at the Mn M-edge, we show that the re-orientation timescale spans from 12 ps to 24 ps, depending on the laser excitation fluence. We then verify these data with a simple model of spin precession with a temperature-dependent magnetocrystalline anisotropy field to show that the spin reorientation timescale is consistent with the reorientation being driven by very large anisotropies energies on approximately $\approx$ meV scales. Promisingly, the model predicts a possibility of 180o reorientation of the out-of-plane moment over a range of excitation fluences. This could facilitate optically controlled magnetization switching between very stable ground states, which could have useful applications in spintronics or data storage.