Anomalous Hall Effect in Antiferromagnetic MnTe

The presence of magnetic field-induced voltage is a prerequisite for many applications. Often, as e.g. in the case of giant magnetoresistance systems, it is related to magnetic reorientation of ferromagnetic layers. There is an ongoing effort to reach ferromagnetic functionalities in the antiferromagnetic (AF) materials, knowing that they are far more robust to magnetic environment and enable faster magnetization switching. One of promising effects may be the Anomalous Hall Effect (AHE), with presence of non-zero Hall voltage in the absence of magnetic field.<br/>Anomalous Hall effect has been confirmed in various antiferromagnetic oxides, where because of their insulating character Pt layer was used to reveal the AHE. There are just a few conducting AFs, where current may be passed directly though the antiferromagnetic material. Here we focus on a semiconductor: hexagonal MnTe. It has a high Neel temperature of 307 K and a bandgap of 1.3 eV. Haing been studied in the 60-ies, it has recently been rediscovered [1] with the prediction of large spin splitting [2], related to spin-group symmetry (within the so-called altermagnets). First observation of the AHE in this material were shown in thin films [3]. We are based on bulk samples, having no undesired parasitic background effects related to the substrate. Modifying the growth technique and using doping we were able to tune room temperature resistivity of our bulk crystals from 0.05 Ohm*cm to about 20 Ohm*cm. We clearly demonstrate the presence of the AHE at the room temperature, with a hysteresis loop with relatively large cohersive field of ~1T. The sign of the AHE hysteresis is opposite than in the case of thin films. The presence of the AHE is understood in terms of nonvanishing Berry curvature and also is predicted by the Dzyaloshinskii–Moriya type interaction, which explains also weak ferromagnetic-like signal revealed in the magnetization studies [4]. The studies of how the doping level (i.e. Fermi level position) affects the AHE will be presented and compared with the theoretical predictions, verifying this promising path for spintronic applications.<br/><br/><br/>[1] D. Kriegner et al., <i>Phys. Rev. B </i><b>96</b>, 214418(2017),<br/>[2] L. Šmejkal et al., <i>Phys. Rev. X</i><b>12</b>, 040501 (2022),<br/>[3] R. D. G. Betancourt et al., <i>Phys. Rev. Lett.</i><b>130</b>, 036702 (2023),<br/>[4] K. P. Kluczyk et al., Phys. Rev. B <b>110</b>, 155201 (2024)