The Effect of Nickel Substitution on Magnetism in the Layered van der Waals Ferromagnet Fe$_3$GeTe$_2$

TL;DR

This study investigates how substituting nickel for iron in the layered ferromagnet Fe$_3$GeTe$_2$ affects its magnetic properties, revealing a transition from ferromagnetic order to a cluster glass phase with increasing Ni content.

Contribution

It provides the first systematic analysis of Ni substitution effects on the structure and magnetism of Fe$_3$GeTe$_2$, including detailed characterization of magnetic phase evolution.

Findings

Ferromagnetic transition temperature decreases with Ni substitution.

Magnetic order evolves from ferromagnetic to cluster glass phase.

Structural integrity is maintained despite Ni substitution.

Abstract

We have grown a series of nickel substituted single crystals of the layered ferromagnet (FM) Fe$_3$GeTe$_2$. The large single crystalline samples of (Fe$_{1-x}$Ni$_x$)$_3$GeTe$_2$ with $x = 0-0.84$ were characterized with single crystal X-ray diffraction, magnetic susceptibility, electrical resistance and muon spin spectroscopy. We find Fe can be continuously substituted with Ni with only minor structural variation. In addition, FM order is suppressed from $T_\mathrm{C}=212$~K for $x=0$ down to $T_\mathrm{C}=50$~K for $x=0.3$, which is accompanied with a strong suppression of saturated and effective moment, and Curie-Weiss temperature. Beyond $x=0.3$, the FM order is continuously smeared into a FM cluster glass phase, with a nearly full magnetic volume fraction. We attribute the observed change in the nature of magnetic order to the intrinsically disordered structure of Fe$_3$GeTe$_2$ and subsequent dilution effects from the Ni substitution.