A phenomenological model for the rare-earth contribution to the magnetic anisotropy inRFe11Ti and RFe11TiH

Abstract

A phenomenological model based on the interactions between the crystal field and the 3d–4fexchange interactions has been developed to explain the zero-kelvin magnetic anisotropy of theRFe11Ti compounds andtheir hydrides, RFe11TiH, where R is a rare-earth element. In most cases, this modelalso predicts the existence of a spin reorientation either in theRFe11Ti orthe RFe11TiH compounds. A more advanced model, that takes into account the temperature dependenceof the anisotropy coefficient, expressed in terms of generalized Brillouin functions, hasalso been developed and used to predict the spin-reorientation temperatures ofseveral of the compounds. A set of crystalline electric field parameters for theRFe11Ti andRFe11TiH compounds,with R = Pr, Nd, Sm, Tb, Dy, Ho and Er, has been obtained. With these parameters the magnetic phase diagramsof the RFe11Ti and RFe11TiH compounds have been reproduced. More specifically, the spin-reorientation temperaturesand the temperature dependence of the magnetocrystalline anisotropy are correctlypredicted when the higher-order terms of the crystal field are included in the model.Further, changes in the magnetocrystalline anisotropy that take place upon hydrogenationhave been explained by a substantial decrease in the first-order crystal field coefficient,A20, accompanied by a smaller decrease of the third-order coefficient,A60.ErFe11TiH andNdFe11TiH exhibit a smallerdecrease in their Anm parameters upon hydrogenation than do the remaining rare-earth compounds.