Evidence for itinerant electron-local moment interaction in Li-doped $\alpha$-MnTe

TL;DR

This study investigates how lithium doping affects the magnetic and electronic properties of $ ext{α}$-MnTe, revealing a spin reorientation, increased itinerant carriers, and a new magnon decay channel driven by carrier interactions, while confirming the robustness of local moments.

Contribution

It provides experimental evidence of carrier-induced magnon decay and spin reorientation in Li-doped $ ext{α}$-MnTe, highlighting the role of carrier-spin interactions in altermagnetic materials.

Findings

Li doping causes spin reorientation from in-plane to out-of-plane.

Doping increases itinerant carrier density without altering the band structure significantly.

High-energy spin wave lifetime decreases abruptly near zone boundary with doping.

Abstract

We use inelastic neutron scattering (INS) and angle-resolved photoemission spectroscopy (ARPES) to study the impact of Li doping on the semiconducting altermagnet $\alpha$-MnTe. Introducing Li results in a spin reorientation from in-plane to out-of-plane direction and increases the density of itinerant carriers. While our ARPES measurements do not indicate any notable doping-induced changes in the electronic band structure or the magnitude of the altermagnetic band splitting, our INS measurements reveal an abrupt carrier-induced decrease in the spin wave lifetime near the zone boundary at high energies. This finding is consistent with a new magnon decay channel driven by doping-induced subtle changes in the band structure and enhanced interactions between Mn$^{2+}$ local moments and itinerant electrons. By extracting the local dynamic susceptibility from INS spectra and applying the total moment sum rule, we find that both undoped and Li-doped $\alpha$-MnTe exhibit the full expected Mn$^{2+}$ local moment of $\approx5.9~\mu_\mathrm{B}$ with $S=5/2$. These findings suggest that $\alpha$-MnTe hosts robust local-moment altermagnetism which shows a breakdown at high energies upon addition of itinerant carriers, highlighting the importance of carrier-spin coupling in magneto-transport and spin dynamic properties of altermagnets even in the dilute-carrier limit.