Description of magnetic anisotropy and spin–reorientation transitions in NdFe12−xMox and NdFe12−xMoxN (x=1.0, 2.0, 3.0)

Abstract

NdFe12−xMox and NdFe12−xMoxN (x=1,2,3) were investigated by studying the anisotropy field and the temperature or field-induced spin–reorientation transitions. The temperature dependence of the magnetic anisotropy field was determined by means of the singular-point-detection technique for polycrystalline aligned samples. A theoretical explanation of the magnetic anisotropy and the magnetic phase transitions is given. The temperature dependencies of the rare-earth anisotropy constants were calculated using the single-ion model within linear theory. Fitting the experimental data, a set of crystal-field and exchange-field parameters for Nd3+ ions was deduced. A first-order spin–reorientation transition from uniaxial to conical phase and a type-2 first-order magnetization process in the perpendicular field are calculated for NdFe11Mo. A canted magnetic structure and a type-1 first-order magnetization process in the axial field are predicted for NdFe12−xMoxN. A change of rare-earth anisotropy after nitrogenation was explained by a bonding charge and a superposition model. The calculated temperature dependence of the anisotropy fields in NdFe12−xMoxN is in good agreement with the experimental data over a wide temperature range.