A phenomenological model for the rare-earth contribution to the magnetic anisotropy in RFe11Ti and RFe11TiH

Abstract

A phenomenological model based on the interactions between the crystal field and the 3d-4f exchange interactions has been developed to explain the zero-kelvin magnetic anisotropy of the RFenTi compounds and their hydrides, RFenTiH, where R is a rare-earth element. In most cases, this model also predicts the existence of a spin reorientation either in the RFenTi or the RFenTiH compounds. A more advanced model, that takes into account the temperature dependence of the anisotropy coefficient, expressed in terms of generalized Brillouin functions, has also been developed and used to predict the spin-reorientation temperatures of several of the compounds. A set of crystalline electric field parameters for the RFenTi and RFenTiH compounds, with R = Pr, Nd, Sm, Tb, Dy, Ho and Er, has been obtained. With these parameters the magnetic phase diagrams of the RFenTi and RFe11TiH compounds have been reproduced. More specifically, the spin-reorientation temperatures and the temperature dependence of the magnetocrystalline anisotropy are correctly predicted when the higher-order terms of the crystal field are included in the model. Further, changes in the magnetocrystalline anisotropy that take place upon hydrogenation have 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 and NdFe11TiH exhibit a smaller decrease in their Anm parameters upon hydrogenation than do the remaining rare-earth compounds.