Structural, magnetic, and Mossbauer spectral properties of Pr2Fe17Hx wherex is 1, 2, and 3

The 295 K unit cell parameters of Pr2Fe17Hx, where x is 0, 1, 2, and 3, hav e been determined by x-ray diffraction. Upon hydrogenation, the unit cell v olume expands anisotropically with a 1.2% expansion of the a axis and no ex pansion of the c axis for x = 3. The Curie temperatures are 286, 374, 440, and 484 K, for x = 0, 1, 2, and 3, respectively. The Mossbauer spectra have been measured between 4.2 and 295 K, and the spectra of Pr2Fe17H and Pr2Fe 17H2, obtained above 80 K, and those of Pr2Fe17H3, obtained above 120 K, ha ve been analyzed with a seven sextet model, a model which corresponds to ba sal magnetic anisotropy. The Mossbauer spectra of Pr2Fe17H3 change dramatic ally upon cooling below 80 K, and between 4.2 and 75 K they are well fit wi th a four sextet model which corresponds to axial magnetization. Between 80 and 120 K, the spectra are very complex and, hence, the Mossbauer spectra reveal a spin reorientation which occurs between 80 and 120 K in Pr2Fe17H3. (C) 1999 American Institute of Physics. [S0021-8979(99)55908-2].