A neutron diffraction and Mössbauer spectral study of the magnetic spinreorientation in Nd6Fe13Si

Abstract

Powder neutron diffraction and Mössbauer spectral studies havebeen carried out on Nd6Fe13Si between 2–295 K. The nuclearneutron scattering shows that Nd6Fe13Si has the tetragonalI4/mcmcrystal structure at all temperatures. A collinear antiferromagnetic structure with thewavevector q = (0, 0, 1) is observed below the Néel temperature of 421 K. A spin reorientation isobserved at ∼100 K in both the neutron diffraction patterns and the Mössbauer spectra.Above and below 100 K, the magnetic moments of the four iron and the twoneodymium crystallographic sites are ferromagnetically coupled within one block alongthe caxis and the resulting magnetic moment of this block isantiferromagnetically coupled with that of the adjacent block along thecaxis through a layer of silicon atoms. Above and below 100 K, themagnetic moments are found to be parallel or very close to thec axis and within orclose to the (a, b)basal plane of the tetragonal unit cell, respectively. This first-order spontaneouszero-field spin reorientation occurs cooperatively and involves both theneodymium and iron magnetic moments. The powder neutron diffractionbetween 10 and 200 K indicates anisotropic lattice changes associatedwith a change in the magnetoelastic coupling in this compound. TheMössbauer spectral hyperfine parameters are those expected for axial andbasal magnetization directions in Nd6Fe13Si and further indicate theexistence of a 75% basal and 25% axial mixed magnetic phase even at4.2 K, a mixed magnetic phase which results from the influence of thesecondary ferromagnetic Nd2Fe17 phase on the primary Nd6Fe13Si phase.