Antiferromagnetic order in Co-doped Fe$_5$GeTe$_2$ probed by resonant magnetic x-ray scattering

TL;DR

This study uncovers an antiferromagnetic order in Co-doped Fe$_5$GeTe$_2$, revealing a high transition temperature and the role of Co moments, using resonant magnetic x-ray scattering.

Contribution

It provides the first detailed characterization of AFM order in Co-doped Fe$_5$GeTe$_2$ and highlights the influence of Co magnetic moments on the magnetic ground state.

Findings

AFM order with $T_N$ ~ 340 K identified.

Co magnetic moments contribute to the magnetic order.

In-plane magnetic fields polarize spins without creating incommensurate textures.

Abstract

The quasi-two-dimensional van der Waals magnet Fe$_{5-\delta}$GeTe$_2$ has emerged as a promising platform for electronic and spintronic functionalities at room temperature, owing to its large ferromagnetic ordering temperature $T_{\text{C}}$ $\sim$ 315 K. Interestingly, by cobalt (Co) substitution of iron in F5GT, $i.e.$ $({\text{Fe}}_{1-x}{\text{Co}}_x)_{5-\delta}{\text{GeTe}}_2$ (Co-F5GT), not only can its magnetic transition temperature be further enhanced, but the magnetic and structural ground states can also be tuned. Specifically, an antiferromagnetic (AFM) order is induced beyond the Co doping level $x \ge 0.4$. Here, we investigate the magnetic properties of a Co-F5GT single crystal at $x = 0.45(1)$, by utilizing the element specific, resonant magnetic x-ray scattering technique. Our study reveals an A-type, Ising-like AFM ground state, with a transition temperature $T_{\text{N}}$ $\sim$ 340 K. In addition, our work unveils an important contribution from Co magnetic moments to the magnetic order. The application of the in-plane magnetic fields gradually polarize the spin moments along the field direction, but without inducing incommensurate spin texture(s).