Hyperfine field and isomer shift evolution in hydrogenated Nd-Fe-B alloy

RE(2) Fe(14)B (RE = rare earth) materials are capable of absorbing hydrogen to forma stable solid solution at room temperature. Hydrogenation produces a number of significant changes in the hyperfine interactions. In this work. (57)Fe Mossbauer effect spectroscopy and X-ray diffraction measurements were performed on Nd(14.0)Hf(0.08)Fe(78.9)B(7.00) alloys submitted to thermal treatment in hydrogen atmosphere. A non-linear increase of the hyperfine fields and isomer shifts with hydrogen concentration was observed. The hyperfine parameters of the Sj(1) site exhibit a rather different evolution than those experienced by the other major sites (8j(2), 16k(1), 16k(2)). The origin of the hyperfine field enhancement is analyzed in terms of volume expansion and H nearest neighbors to the Fe sites. A linear expression on these two effects to give account of isomer shift evolution for 8j(1) site is given.