Magnetic structure and phase stability of the van der Waals bonded ferromagnet Fe3-xGeTe2

TL;DR

This study investigates the magnetic structure and phase stability of Fe3-xGeTe2, revealing how Fe content influences magnetic properties and identifying multiple charge carriers affecting electrical transport.

Contribution

It provides detailed insights into the magnetic order, phase diagram, and the impact of Fe deficiency in Fe3-xGeTe2 using various experimental techniques.

Findings

Ferromagnetic order with moments of 1.11μB/Fe aligned along the c-axis at 4K.

Reduced Fe content lowers Curie temperature, magnetic anisotropy, and magnetization.

Multiple carrier types contribute to electrical transport in Fe3-xGeTe2.

Abstract

The magnetic structure and phase diagram of the layered ferromagnetic compound Fe$_3$GeTe$_2$ has been investigated by a combination of synthesis, x-ray and neutron diffraction, high resolution microscopy, and magnetization measurements. Single crystals were synthesized by self-flux reactions, and single crystal neutron diffraction finds ferromagnetic order with moments of 1.11(5)$\mu_B$/Fe aligned along the $c$-axis at 4K. These flux-grown crystals have a lower Curie temperature $T_{\textrm{c}}\approx$150K compared to crystals previously grown by vapor transport ($T_{\textrm{c}}$=220K). The difference is a reduced Fe content in the flux grown crystals, as illustrated by the behavior observed in a series of polycrystalline samples. As Fe-content decreases, so does the Curie temperature, magnetic anisotropy, and net magnetization. In addition, Hall effect and thermoelectric measurements on flux-grown crystals suggest multiple carrier types contribute to electrical transport in Fe$_{3-x}$GeTe$_2$ and structurally-similar Ni$_{3-x}$GeTe$_2$.