155Gd Mössbauer effect and magnetic properties of Gd2Co17Nx

The ternary nitride Gd₂Co₁₇N_x (with x close to 3) was prepared by charging Gd₂Co₁₇ with nitrogen gas. We have studied this compound by means of X-ray diffraction, magnetic measurements and ¹⁵⁵Gd Mössbauer spectroscopy. Upon charging, there is an increase in unit-cell volume of about 6.3%. The preferred moment direction changes from easy plane to easy axis and there is a small reduction in the Co-sublattice moment. From the analysis of the ¹⁵⁵Gd Mössbauer spectrum of Gd₂Co₁₇N_x it is derived that the electric-field gradient at the Gd nuclei is 14.9 × 10²¹ V/m², which is somewhat larger than that found at the Gd sites in Gd₂Fe₁₇N_x. The experimental value of V_zz is in good agreement with self-consistent band structure calculations made for Gd₂Co₁₇ and its ternary nitride. The results of these calculations have also been used to discuss the changes in magnetic moment upon nitrogen take-up.