MOSSBAUER-EFFECT EVIDENCE OF INFLUENCE OF THORIUM ON THE SPIN REORIENTATION IN (ER1-XTHX)(2)FE14B INTERMETALLIC COMPOUNDS

The spin reorientation in the (Er1-xThx)(2)Fe14B system was observed b y Fe-57 Mossbauer spectroscopy and magnetic measurements. The phenomen on originates from a competition between the magnetic anisotropies of the iron and rare earth sublattices, the latter being altered by subst itution of thorium for erbium. The spin transition temperature was der ived from magnetic measurements. Its value is lowered by magnetic dilu tion of the rare earth crystal sublattice, due to substitution of thor ium for erbium. The Fe-57 Mossbauer effect measurements were carried o ut at room and liquid nitrogen temperatures. Owing to the influence on the shape of Mossbauer spectra of the combined electric quadrupole an d 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 evid ence that the spin reorientation process proceeds not at a discrete te mperature but in a wide temperature range. The discrete values of the Fe-57 hyperfine interaction parameters, derived from Mossbauer absorpt ion spectra, are consistent with localised interactions of iron atoms with their nearest neighbours. It was found that substitution of thori um for erbium slightly reduces the hyperfine magnetic fields at iron s ites and has only a minute influence on the values of the isomer shift s and quadrupole interactions.