A Mössbauer spectral study of the Nd6Fe13X compounds where X is Si, Cu, Ag, and Au

The Mössbauer spectra of Nd6Fe13X, where X is Si, Cu, Ag, and Au, have been measured between 85 and 435 K. An analysis of the spectra of Nd6Fe13X, where X is Cu, Ag, and Au in terms of five sextets, indicates that the iron moments lie in the basal plane of the unit cell. The assignment of the five sextets to the five magnetically inequivalent sites in the structure is based on a correlation between the isomer shift and the Wigner–Seitz cell volume for all iron sites, between the isomer shift and the hyperfine field for each site, and the relationship between the hyperfine field at a given iron site and its number of iron near-neighbors. An analysis of the spectra of Nd6Fe13Si reveals that a high temperature magnetic phase, with its moments parallel to the c axis, coexists between 295 and 85 K with a low temperature magnetic phase, with its moments oriented in the basal plane. Hence, Nd6Fe13Si shows a continuous magnetic spin-reorientation from axial towards basal alignment upon cooling.