with broken time-reversal symmetry*

In conventional ferromagnets, the magnitude of anomalous Hall effect is proportional to net magnetization. On the other hand, in recent times, it was theoretically proposed that some antiferromagnets with broken time-reversal symmetry (TRS) can induce large spontaneous Hall effect despite vanishingly small net magnetization. In this study, we investigated the properties of Mn₁₁Ge₈ as a candidate of TRS-broken antiferromagnet. This material was reported to show weak spontaneous magnetization along b-axis, which implies the realization of antiferromagnetic order with broken TRS. By performing detailed magnetization measurement, we identified four distinctive magnetic phases as a function of temperature and magnetic field. We also found that the Hall resistivity profile does not simply scale with net magnetization, implying the additional Hall contribution originating from TRS-broken antiferromagnetic order.