155Gd M/Sssbauer effect studies and magnetic properties of GdFe12_xMOx(Ny)compounds

Structural and magnetic properties of the GdFe12_~MOx compounds having the ThMn12 type of structure were studied. Rare-earth nitrides of the composition GdFe 12-x MOx N y were prepared by the reaction of GdFe12_x MOx with nitrogen gas at 475°C. The crystal structure and lattice constants have been determined for all compounds. The lattice expansion of the nitrogenated compounds is mainly along the a-axis, the Curie temperatures are increased by about 110 K. We investigated the effect of interstitial nitrogen on the magnetic properties and the 155Gd M/Sssbauer spectrum of GdFe12_xMO x. Values of the electric field gradient V~z derived from the quadrupole splitting of the spectra were strongly negative, with Vzz = 21.3 X 1021 V m -2 and Vzz = 19.9 × 1021 V m -2 for x = 1.5 and 3.0, respectively. Nitrogenation is shown to lead to a sign reversal of the 4f as well as of the 3d sublattice anisotropies.