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

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 Dy₂Fe₁₄BH_3.3. 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 Er₂Fe₁₄BH_x) 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.