||関 真一郎 准教授
||Antiferromagnetic materials with broken time-reversal symmetry
||Recently, the concept of spintronics, i.e. the technology that utilizes not only charge but also spin degree of freedom of electrons, has attracted attention as the key to enable the innovative devices with rich functionality.
So far, the spintronics has mainly focused on ferromagnets, where their magnetization and associated time-reversal symmetry breaking allow us to retain, read and write magnetic information. On the other hand, the recent discovery of antiferromagnets with broken time-reversal symmetry suggests that the latter systems can be another platform for the next generation of spintronics.
A typical example is Mn3Sn with non-collinear antiferromagnetic order which breaks time-reversal symmetry. Despite its antiferromagnetic character, this compound shows giant anomalous Hall effect and anomalous Nernst effect, which have previously been reported only in ferromagnetic materials with macroscopic magnetization. Mn3Sn has topological Weyl nodes in its electronic band structure due to time-reversal symmetry breaking , and the associated fictitious magnetic field generated via the quantum Berry curvature plays a role equivalent to magnetization. Such antiferromagnets with broken time-reversal symmetry are expected to have a similar function to ferromagnets due to their fictitious magnetic field, but also with potential advantages specific to antiferromagnets, such as the absence of a magnetization-derived stray field. However, there are still only a few reported examples of time-reversal symmetry broken antiferromagnets, and in particular, the one with the collinear antiferromagnetic order has not been established yet. [4,5]. Therefore, the further search of such materials systems is highly demanded.
In this presentation, I will discuss the current status of our research on such time-reversal symmetry broken antiferromagnets.
 S. Nakatsuji et al., Nature 527, 212 (2015).
 M. Ikhlas et al., Nature Phys. 13, 1085 (2017).
 K. Kuroda et al., Nature Mat. 19, 1090 (2017).
 N. J. Ghimire et al., Nature Comm. 9, 3280 (2018).
 G. Tenasini et al., Phys. Rev. Lett. 2, 023051 (2020).