Strain-tunable Anomalous Hall Effect in hexagonal MnTe

The ability to control time-reversal-symmetry-breaking phases with near-zero net magnetization is central to spintronic design. The hexagonal altermagnet α-MnTe is a prime platform. It has a compensated altermagnetic ground state where the magnetic moments are aligned in each layer and stacked antiparallel along the c axis. However, the presence of three 120° separated in-plane magnetic domains presents a challenge in understanding the origin of anomalous Hall effect (AHE) and the effective control of the altermagnetic state. Here we use neutron scattering to show that a modest compressive uniaxial strain along the next-nearest-neighbor Mn-Mn bond direction detwins α-MnTe into a single in-plane magnetic domain, aligning the in-plane moments along the same direction. Furthermore, we find that uniaxial strain (-0.2% to 0.1%) significantly sharpens the magnetic hysteresis loop and switches the sign of the AHE near room temperature. Combined with our phenomenological model, we argue that these effects result from the modification of the electronic Berry curvature by a combination of both spin-orbit coupling and strain. Our work not only unambiguously establishes the relationship between the in-plane moment direction and the AHE in α-MnTe but also paves the way for future applications in highly scalable, strain-tunable magnetic sensors and spintronic devices.