Pervasive beyond room-temperature ferromagnetism in a doped van der Waals magnet: Ni doped Fe$_5$GeTe$_2$ with $T_{\text{C}}$ up to 478 K

TL;DR

This study demonstrates that doping Fe$_5$GeTe$_2$ with Ni results in pervasive ferromagnetism above room temperature, reaching a record Curie temperature of 478 K, due to structural changes enhancing magnetic coupling.

Contribution

It reports the achievement of record-high ferromagnetic transition temperature in Ni-doped Fe$_5$GeTe$_2$, showing pervasive ferromagnetism across the doping range, which is a novel finding.

Findings

Record high $T_C$ of 478 K in Ni-doped Fe$_5$GeTe$_2$

Pervasive ferromagnetism across the doping phase diagram

Structural alterations likely enhance 3D magnetic couplings

Abstract

The existence of long range magnetic order in low dimensional magnetic systems, such as the quasi-two-dimensional (2D) van der Waals (vdW) magnets, has attracted intensive studies of new physical phenomena. The vdW Fe$_N$GeTe$_2$ ($N$ = 3, 4, 5; FGT) family is exceptional owing to its vast tunability of magnetic properties. Particularly, a ferromagnetic ordering temperature ($T_{\text{C}}$) above room temperature at $N$ = 5 (F5GT) is observed. Here, our study shows that, by nickel (Ni) substitution of iron (Fe) in F5GT, a record high $T_{\text{C}}$ = 478(6) K is achieved. Importantly, pervasive, beyond-room-temperature ferromagnetism exists in almost the entire doping range of the phase diagram of Ni-F5GT. We argue that this striking observation in Ni-F5GT can be possibly due to several contributing factors, in which the structural alteration enhanced 3D magnetic couplings might be critical for enhancing the ferromagnetic order.