Large Anomalous Hall Effect, Non-Vanishing Berry Curvature in (110) FeRh Antiferromagnet Films via Interface Strain.

Abstract

The anomalous Hall effect (AHE) has been understood as a transport phenomenon usually observed in ferromagnetic and non-collinear antiferromagnetic materials where broken time-reversal symmetry combined with spin-orbit coupling produces a net Berry curvature. Combined spatial inversion (P) and time-reversal (T) symmetries forbid an AHE in collinear antiferromagnets. In this study, we demonstrate a pronounced AHE in (110)-oriented FeRh thin films epitaxially grown on Al₂O₃ substrates, even though the films remain collinear antiferromagnetic at low temperatures. Unlike the bulk B2 phase, where PT symmetry enforces the cancellation of Berry curvature, the epitaxial (110) orientation and substrate-induced strain explicitly break the spatial inversion symmetry (P). This symmetry-lowering mechanism, which lifts the PT constraint, enables a finite Berry curvature distribution in momentum space. Consequently, this allows for robust anomalous transverse transport even in the collinear antiferromagnetic regime, providing a new degree of freedom to engineer topological properties in antiferromagnets. First-principles density-functional calculations reproduce the strain-induced Berry curvature and quantitatively account for the measured AHE in the 5-100 K range. Our results show that intrinsic strain can be harnessed to tailor Berry curvature in collinear antiferromagnets, opening a pathway toward antiferromagnetic spintronic applications.