The magnetic domain structures of small crystals

Abstract

The first part of the article describes the calculation of magnetostatic energies (which are necessary to predict the critical sizes of crystals below which domains cease to form) and of the domain spacing or number of domains per crystal. Methods suitable for periodic ‘magnetic charge’ distributions in semi-infinite crystals and for finite distributions are described, and both planar and cylindrical domain walls are included. The reasons for the special interest in small crystals is discussed. The second part presents results on thin crystals of barium ferrite with both extensive and discrete structures; orthoferrite crystals with extensive walls and containing one or two cylindrical domains; and small crystals of gadolinium iron garnet near to the compensation temperature, in which the number of domains is a function of temperature. These results are discussed in the light of the theories outlined.