Fig. 5: Demonstration of antiferromagnetic trichroism.

a–d A sequence of Aʹ images of an X-plane sample for k_X > 0 at 5 K in varying applied fields (μ₀H_Y) of 0 T (a), 0.36 T (b), 0.58 T (c), and then 0 T (d). Here, Aʹ is the variation of absorption coefficient from 50 K (> T_N). E^ω is parallel to the Y axis and light wavelength is 750 nm. The domain pattern at 0 T is slightly changed once μ₀H_Y of 0.58 T is applied, as denoted by yellow circles in (d). Scale bar below (a) is 0.2 mm. e–h A sequence of magnified images of the yellow-box region in (a) in varying μ₀H_Y of 0 T (e), 0.32 T (f), 0.36 T (g), and 0.4 T (h). In (g), a boundary separating L_+Y (blue) and L_−Y (red) domains corresponds to a 180° antiferromagnetic domain wall (AFDW). A L_+X/L_−X domain (L_+X or L_−X or both) is pointed by a black arrow. Scale bar next to (f) is 0.1 mm. i The μ₀H_Y dependence of Aʹ at regions I–VI defined in (e). The yellow rectangle represents a region where the L_+Y, L_−Y, and L_+X/L_−X domain states coexist.