Ferrimagnetic structure in the high-pressure phase of 𝛼−Mn

The 𝛼−Mn phase exhibits a large anomalous Hall effect (AHE) in its pressure-induced weak ferromagnetic (WFM) state, despite its relatively small spontaneous magnetization of ∼0.02𝜇B/Mn. To understand the underlying mechanism behind this AHE, we performed single crystal neutron diffraction measurements at 2.0 GPa to determine the magnetic structure of the WFM phase. Our investigation reveals a ferrimagnetic structure characterized by nearly collinear magnetic moments aligned along the [001] direction at sites I, II, III-1, and IV-1. In contrast, the small moments at sites III-2 and IV-2 lie within the (001) plane. The calculated net magnetization of this magnetic structure, (−0.08±0.10)⁢𝜇B/Mn atom, is in agreement with the experimentally determined spontaneous magnetization. The observation of a magnetic reflection at 𝒒=(0,0,0) satisfies a key condition for the emergence of the AHE.