IRREVERSIBLE ROTATION PROCESSES IN UNIAXIAL FERROMAGNETIC CRYSTALS

The coexistence of two minima in the anisotropy energy of a ferromagnetic crystal allows irreversible rotations of the magnetization vector to occur at a critical value Hcr of the applied magnetic field. These first order magnetization processes (FOMP) are in fact similar to the spin reorientation transitions that take place between different easy directions with changing temperature. The study of FOMP allows precise determinations of the anisotropy constants to be carried out if one knows the relations with the critical parameters. Previous papers give experimental evidence of FOMP in ferrites1 and intermetallic2 compounds together with a preliminary theoretical treatment. In the present work we carry out a complete analysis of this phenomenon in terms of the first three anisotropy constants Ki and coefficients κ21,0, for a uniaxial crystal with field applied parallel or perpendicular to the symmetry axis. Analytical solutions have been found for the case of type 2 FOMP (when final state is below saturation) and for the boundary lines in the phase diagrams of easy directions and FOMP. Computer plots of the critical parameters vs. K2/K1, K3/K1 and x4,0/x2,0, x6.0/x2.0, and application to the FOMP observed at 16 Tesla in the easy cone crystal PrCo5 will be presented. 1G. Asti et al, IEEE Trans. MAG. 14, 883 (1978). 2D. Melville et al, IEEE Trans. MAG 12, 1012 (1976). © 1979, American Institute of Physics. All rights reserved.