Magnetism and crystal field properties of the RE2Fe14BHxalloys (RE=Y, Ce, Dy, Er) from Mossbauer spectroscopy

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Abstract
57Fe and 161Dy Mossbauer results are reported in the RE2Fe14B (RE=Y, Ce, Dy, Er) alloys and some of the corresponding hydrides. An analysis of the 57Fe hyperfine parameters is performed consistently in the paramagnetic and ordered phases of the compounds, providing in particular the hyperfine fields (i.e. the local magnetic moments) at the various crystallographic sites. The 161Dy hyperfine fields reveal fairly pure mod J=15/2) ground multiplets in Dy2Fe14B and Dy2Fe14BH3.3. The 161Dy quadrupole interactions are interpreted to provide empirical estimates for the second-order crystal field parameter B20 at the two Dy sites. Point charge calculations suggest highly anisotropic B2 tensors. A spin reorientation is observed in Er2Fe14B (and Er2Fe14BHx) whereas in Dy2Fe14B, Y2Fe14B and Ce2Fe14B a collinear spin structure along the c axis is maintained down to 4.2K. The directions of anisotropy along the series of compounds and the spin reorientation phenomena are discussed on the basis of the proposed crystal field parameters.