Domain structures in haematite (α-Fe₂O₃)

Abstract

Magnetic domain structures in basal-plane platelets of α-Fe₂O₃ have been studied by X-ray topography in fields up to 56kAm⁻¹. Three types of wall were found: ferromagnetic walls perpendicular to the basal plane, in-plane 60° antiferromagnetic Bloch walls and walls inclined to the trigonal axis containing an a direction in the basal plane. Inclined walls showed dynamical diffraction fringes and became invisible when the diffraction vector was perpendicular to the wall trace. The first and third. types of wall were seen only in low fields (less than 1·5 k Am⁻¹) and strong interactions with lattice defects occurred. Both were identified as 180° ferromagnetic boundaries. The Bloch walls also were pinned by inversion twin boundaries, leading to the wall being tilted out of the basal plane. Tilting always occurred in the same direction, irrespective of the sense of the field applied parallel to the twofold axis. Complex interdigital domain structures were observed on the tilted walls which, it is suggested, reduce the magnetostatic energy associated with the weak ferromagnetic component. The spacing of these structures varied inversely with field. Measurements of the wall position as a function of field supported the identification of 60° antiferromagnetic walls.