COMPETING ANISOTROPIES AND 1ST-ORDER MAGNETIZATION PROCESSES

The analysis of the canting model theory up to the fourth order, including the in-plane contribution to the total anisotropy, is presented. The origin of the first-order magnetization process (FOMP) is well explained in terms of competing anisotropies. The fourth-order terms are essential for the presence of a FOMP; in fact, computer simulations, with only second-order terms, show regular magnetization curves, and the representation, in terms of equivalent single sublattice anisotropy constant K@B|i, explains the origin, from the competition, of the high-order terms, but they are not strong enough to produce FOMP transitions. An analysis of the effects of each parameter in the energy expression is given, in particular the behavior of the magnetization curves and the evolution of the easy cone are studied. An analytical expression for the anisotropy field and of the energy instability at zero field (origin of easy cone) has been derived. As an application of the model, an analysis of the magnetization curves, in hard direction of single crystals of PrCo5, Nd2Fe14B, and Pr2Fe14B is given; the good agreement with experimental results shows that the above model explains well the origin of the spin reorientation and of the FOMP transitions observed in these compounds.