Spontaneous Hall effect induced by altermagnetic order at room temperature

Today, magnetic information is mostly stored in ferromagnets, where the up and down spin states are distinguishable due to time-reversal symmetry breaking. In these two states, electric current induces the opposite sign of transverse voltage in proportion to magnetization (anomalous Hall effect), and this phenomenon has been widely used for electrical readout of the up and down spin states in ferromagnets. In contrast, the aforementioned functions cannot be expected in conventional antiferromagnets with collinear antiparallel (up-down) spin configuration, because of its macroscopic time-reversal symmetry (TRS) and lack of macroscopic magnetization. According to recent theories, however, it has been predicted that such a collinear antiferromagnetic order can often host sizable spontaneous Hall effect even without net magnetization or external magnetic field, when combined with a crystal lattice with appropriate symmetry. Such a TRS-broken collinear antiferromagnet is often termed “altermagnet”.

In this talk, I report the experimental observation of spontaneous Hall effect in a collinear antiferromagnet at room temperature [1]. In this compound, the up-down and down-up spin states induce the opposite sign of spontaneous Hall effect. Our detailed analysis suggests that the observed spontaneous Hall signal does not reflect magnetization, but rather originates from the fictitious magnetic field associated with TRS-broken antiferromagnetic order. The present results pave the way for the electrical reading and possible writing of the up-down and down-up spin states in conductive systems at room temperature, which suggests that TRS-broken collinear antiferromagnets may serve as a unique information medium to realize nontrivial spintronic responses with vanishingly small magnetization.

[1] R. Takagi, R. Hirakida, Y. Settai, R. Oiwa, H. Takagi, A. Kitaori, K. Yamauchi, H. Inoue, J. Yamaura, D. Nishio-Hamane, S. Itoh, S. Aji, H. Saito, T. Nakajima, T. Nomoto, R. Arita, S. Seki, Nature Materials (in press)