NEAR-SURFACE MAGNETIC-STRUCTURES IN IRON BORATE

Surface magnetism on natural non-basal faces of iron borate monocrystals was found and analysed by means of the magneto-optical and Bitter methods. The surface magnetism here is represented by a macroscopical transition magnetic layer, the result of surface magnetic anisotropy. Anisotropy is caused by the change in surface magnetic ion environment symmetry. The erasure of surface magnetism at a face of the (1014)-type takes place in a field of Hc = 1.6 kOe, the same characteristic for faces of the (1110) and (1123)-types is {less-than or approximate} 100 Oe. By measuring the temperature-critical field relationship in the temperature range from 77 K upto the Néel point, it was found that Hc is proportional to the crystal's magnetization. Surface anisotropy energy and the structure of transition magnetic layers are calculated for the analyzed types of faces. The developed theory gives a correct description of surface magnetic anisotropy's symmetry, yields the Hc field value order which agrees with the experimentally determined one, and also explains the temperature-critical field relationship. © 1990.