Spontaneous Hall and Nernst effects in antiferromagnets

The anomalous Hall effect and its thermoelectric counterpart, the anomalous Nernst effect, were for a long time believed to be exclusively present in ferromagnetic materials. The development in the past years, however, revealed that these effects can be finite also in certain non-collinear antiferromagnets owing to the non-trivial topology of their band structure. A typical representative of this class of antiferromagnets is Mn₃Sn. In the first part of this talk, we therefore discuss magneto thermal transport measurements in Mn3Sn thin films. We demonstrate that the local magneto-thermal response can be employed for a spatially resolved visualization of the magnetic properties of the antiferromagnet [1]. In the second part of the talk, we then address mechanisms for spontaneous Hall effects (i.e. a Hall effect present in absence of magnetic fields), including the crystal Hall effectrecently proposed by theory [2] and corroborated by first experimental indications in RuO₂ [3]. This so far overlooked mechanism enables a spontaneous Hall effect arising from the crystal and spin symmetry of a particular compound, which tremendously broadens the pool of materials in which spontaneous Hall and Nernst effects can be expected. We finally introduce one particular example of a collinear antiferromagnet Mn₅Si₃ in which a finite spontaneous Hall effect is enabled via yet another combination of spin-space symmetry, and address the various contributions to the Hall signal together with their microscopic origins [4].

[1] Reichlova et al., Nature Communications 10, 5459 (2019)
[2] Smejkal et al., Science Advances 6, eaaz8809 (2020)
[3] Feng et al., arXiv:2002.08712 (2020)
[4] Reichlova et al., arxiv.org/abs/2012.15651