Mössbauer effect evidence of influence of thorium on the spin reorientation in (Er1−xThx)2Fe14B intermetallic compounds

Abstract

The spin reorientation in the (Er1−xThx)2Fe14B system was observed by 57Fe Mössbauer spectroscopy and magnetic measurements. The phenomenon originates from a competition between the magnetic anisotropies of the iron and rare earth sublattices, the latter being altered by substitution of thorium for erbium. The spin transition temperature was derived from magnetic measurements. Its value is lowered by magnetic dilution of the rare earth crystal sublattice, due to substitution of thorium for erbium. The 57Fe Mössbauer effect measurements were carried out at room and liquid nitrogen temperatures. Owing to the influence on the shape of Mössbauer spectra of the combined electric quadrupole and magnetic dipole hyperfine interactions, it was possible to show, in a simple manner, that a spin reorientation phenomenon had taken place between 78 and 295 K in the investigated compounds. There is also evidence that the spin reorientation process proceeds not at a discrete temperature but in a wide temperature range. The discrete values of the 57Fe hyperfine interaction parameters, derived from Mössbauer absorption spectra, are consistent with localised interactions of iron atoms with their nearest neighbours. It was found that substitution of thorium for erbium slightly reduces the hyperfine magnetic fields at iron sites and has only a minute influence on the values of the isomer shifts and quadrupole interactions.