Antiferromagnetic Domain Walls and the Magnetization Process in α−Fe2O3

Abstract

The magnetic properties of α−Fe₂O₃ are of interest since it is a prototype of the class of antiferromagnetic substances possessing a weak ferromagnetism superimposed on the normal antiferromagnetic susceptibility. Two possible sources of the weak ferromagnetism, i.e., moment bearing antiferromagnetic domain walls and special ferrimagnetic forms of Fe₂O₃, are considered from the standpoint of their magnetization processes. It is noted that moment bearing or nonmoment bearing domain walls may be required by the presence of certain edge and screw dislocations. The net moment of a domain wall may reverse by a wall displacement process or by the motion of a boundary within the domain wall, i.e., a Bloch line. Measurement of the rotational hysteresis in α−Fe₂O₃ proves that the weak ferromagnetism is not caused by a nonepitaxial second‐phase ferrimagnetic impurity. It is concluded that the behavior of α−Fe₂O₃ at room temperature can be ascribed to moment bearing domain walls magnetizing by Bloch line motion, and/or ferrimagnetic Fe₂O₃ basal intergrowths in exchange contact with the antiferromagnetic lattice (Meiklejohn effect). The low‐temperature state can also be qualitatively understood with this model.