Spectral Evidence for Local-Moment Ferromagnetism in van der Waals Metals Fe$_3$GaTe$_2$ and Fe$_3$GeTe$_2$

TL;DR

This study compares the electronic structures of Fe3GaTe2 and Fe3GeTe2, revealing that their ferromagnetism is likely driven by electron correlations rather than itinerant electrons, challenging the conventional Stoner model.

Contribution

The paper provides a systematic spectroscopic and theoretical comparison of two Fe-based vdW ferromagnets, highlighting the role of electron correlations in their magnetic properties.

Findings

Fe3GaTe2 shows no band shift across T_C, unlike Fe3GeTe2.

Weak temperature dependence suggests non-itinerant ferromagnetism.

Expanded hole pockets indicate additional hole carriers in Fe3GaTe2.

Abstract

Magnetism in two-dimensional (2D) materials has attracted considerable attention recently for both fundamental understanding of magnetism and their tunability towards device applications. The isostructural Fe$_3$GeTe$_2$ and Fe$_3$GaTe$_2$ are two members of the Fe-based van der Waals (vdW) ferromagnet family, but exhibit very different Curie temperatures (T$_C$) of 210 K and 360 K, respectively. Here, by using angle-resolved photoemission spectroscopy and density functional theory, we systematically compare the electronic structures of the two compounds. Qualitative similarities in the Fermi surface can be found between the two compounds, with expanded hole pockets in Fe$_3$GaTe$_2$ suggesting additional hole carriers compared to Fe$_3$GeTe$_2$. Interestingly, we observe no band shift in Fe$_3$GaTe$_2$ across its T$_C$ of 360 K, compared to a small shift in Fe$_3$GeTe$_2$ across its T$_C$ of 210 K. The weak temperature-dependent evolution strongly deviates from the expectations of an itinerant Stoner mechanism. Our results suggest that itinerant electrons have minimal contributions to the enhancement of T$_C$ in Fe$_3$GaTe$_2$ compared to Fe$_3$GeTe$_2$, and that the nature of ferromagnetism in these Fe-based vdW ferromagnets must be understood with considerations of the electron correlations.