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Description
Hematite (α-Fe₂O₃) has recently attracted attention as a candidate altermagnet, a phase that combines zero net magnetization with symmetry-imposed spin splitting [1,2]. In this work, we examine how the orientation of the Néel vector (n) governs the transport and magneto-optical responses of collinear altermagnetic α-Fe₂O₃. By combining magnetic space group (MSG) analysis with first-principles calculations, we show that both the anomalous Hall conductivity (AHC) and the magneto-optical Kerr effect (MOKE) depend sensitively on symmetry. When n ∥ [001] (MSG No. 167.103), the antisymmetric conductivity tensor components are forbidden, so the AHC and MOKE vanish. However, reorienting n along [010] (MSG No. 15.89) or [110] (MSG No. 2.1) alters the MSG constraints and allows antisymmetric conductivity, thereby switching on finite AHC and MOKE responses. These results establish symmetry-based selection rules for observing Hall and Kerr responses in collinear altermagnetic hematite.
[1] L. Šmejkal, et al., Nat. Rev. Mater. 7, 4 82 (2022).
[2] L. Šmejkal, et al., Phys. Rev. X. 12, 040501 (2022).
