Anomalous Hall effect induced by Berry curvature in topological nodal-line van der Waals ferromagnet Fe$_4$GeTe$_2$

TL;DR

This paper reports the discovery of a large anomalous Hall effect in Fe$_4$GeTe$_2$, driven by Berry curvature from SOC-induced gaped nodal lines, highlighting its potential for 2D spintronics.

Contribution

It demonstrates the intrinsic Berry curvature origin of the large AHC in Fe$_4$GeTe$_2$, a near-room-temperature ferromagnetic vdW material, with unprecedented Hall angle and Hall factor.

Findings

Large anomalous Hall conductivity (~490 Ω^{-1}cm^{-1}) at 2 K.

Berry curvature from SOC gaped nodal lines causes the AHC.

Record-high anomalous Hall angle (~10.6%) and Hall factor (~0.22 V^{-1}).

Abstract

The exploration of nontrivial transport phenomena associated with the interplay between magnetic order and spin-orbit coupling (SOC), particularly in van der Waals (vdW) systems has gained a resurgence of interest due to their easy exfoliation, ideal for two-dimensional (2D) spintronics. We report the near room temperature quasi-2D ferromagnet, Fe$_4$GeTe$_2$ from the iron-based vdW family (Fe$_n$GeTe$_2$, $n$=3,4,5), exhibiting a large anomalous Hall conductivity (AHC), $\sigma^A_{xy}$ $\sim$ 490 $\Omega^{-1}\textrm{cm}^{-1}$ at 2 K. The near quadratic behavior of anomalous Hall resistivity ($\rho^{A}_{xy}$) with the longitudinal resistivity ($\rho_{xx}$) suggests that a dominant AHC contribution is coming from an intrinsic Berry curvature (BC) mechanism. Concomitantly, the electronic structure calculations reveal a large BC arising from SOC induced gaped nodal lines around the Fermi level, governing such large AHC property. Moreover, we also report an exceptionally large anomalous Hall angle ($\simeq$ 10.6\%) and Hall factor ($\simeq$ 0.22 V$^{-1}$) values which so far, are the largest in compared to those for other members in this vdW family.