Unusual magnetization process in haematite investigated by synchrotron radiation diffraction imaging

The magnetization process of a nearly perfect crystal of haematite is inves tigated through the observation of domain wall evolution in an applied magn etic field, by white-beam X-ray section topography. The sample is a (111) p latelet. The walls are nearly parallel to its main surface. Their contrast changes dramatically with increasing field, but their locations are not alt ered very much during most of this process. These experimental facts are in terpreted as corresponding to a magnetization process which occurs mainly b y spin rotation within the domains. The very small basal plane anisotropy o f haematite and the pinning of the walls by defects results in this unusual magnetization process, which differs from the standard process for ferroma gnets.