Anomalous Hall effect induced by Berry curvature in the topological nodal-line van der Waals ferromagnet Fe4GeTe2

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, ${\mathrm{Fe}}_{4}{\mathrm{GeTe}}_{2}$ from the iron-based vdW family (${\mathrm{Fe}}_{n}{\mathrm{GeTe}}_{2}, n=3$,4,5), exhibiting a large anomalous Hall conductivity (AHC), ${\ensuremath{\sigma}}_{xy}^{A}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}\phantom{\rule{0.16em}{0ex}}490\phantom{\rule{0.16em}{0ex}}{\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}{\text{cm}}^{\ensuremath{-}1}$ at 2 K. The near quadratic behavior of anomalous Hall resistivity (${\ensuremath{\rho}}_{xy}^{A}$) with the longitudinal resistivity (${\ensuremath{\rho}}_{xx}$) 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 gapped nodal lines around the Fermi level, governing such large AHC property. Moreover, we also report an exceptionally large anomalous Hall angle ($\ensuremath{\simeq}10.6$%) and Hall factor ($\ensuremath{\simeq}0.22 {\mathrm{V}}^{\ensuremath{-}1}$) values which, so far, are the largest in compared to those for other members in this vdW family.