A Mössbauer spectral study of Nd6Fe13X, where X is Cu, Ag, and Au and of the spin reorientation in Nd6Fe13Si

Abstract

The Mössbauer spectra of Nd6Fe13X, where X is Si, Cu, Ag, and Au, have been measured between 80 and 500 K. A model corresponding to a basal alignment of the magnetic moments leads to excellent, internally consistent, fits for the Cu, Ag, and Au compounds. The resulting temperature dependences of the spectral hyperfine parameters are uniform and reveal for each Fe site the expected correlations between the isomer shift and the Wigner–Seitz cell volume and the hyperfine field and the number of Fe near neighbors. For Nd6Fe13Si, a different model must be used because of the presence of a spin reorientation below 155 K. Above 155 K, because of the axial alignment of the moments, and in agreement with the 295 K powder neutron diffraction results, the spectra can be analyzed with four sextets. Below 155 K, five additional sextets are required to fit the spectra because of a progressive transition towards a basal alignment of the Fe moments. At 80 K the mixed magnetic phase is 75% basal and 25% axial, whereas at 110 K the mixture is 50:50. The hyperfine parameters of the basal and axial sextets found for Nd6Fe13Si are consistent with those found for the basal Cu, Ag, and Au compounds and those observed for basal Nd6Fe13Sn. The lattice properties of the compounds, obtained from the temperature dependences of the isomer shift and the spectral absorption area, are consistent with the Wigner-Seitz cell volumes and the bonding of each crystallographically distinct Fe site. The magnetic anisotropy of a variety of Nd6Fe13X compounds is controlled by the s-p hybridization of the Nd–X bonds, a hybridization which is very sensitive to the electronic configuration of X.

Magnetic ordering of the R6Fe13Sn (R=Nd, Pr) compounds studied by neutron diffraction

“…After correction, the latter Fe1 moments are in good agreement with those found for Pr Fe Sn and Nd Fe Sn in the course of the present investigation. Also, there is much better agreement with the large hyper"ne "elds reported in MoK ssbauer investigations for this Fe site [13,14].…”

“…It is also consistent with a model description proposed in Ref. [14] in which the magnetic anisotropy of several Nd Fe X compounds is taken to depend strongly on the mixing of the Nd valence electron states with the valence electron states of the X atoms, which is very sensitive to the electronic con"guration of X. In this model description, the compounds Nd Fe Au and Nd Fe Sn fall into the categories basal plane type anisotropy and uniaxial anisotropy, respectively.…”

“…[14] that the magnetic anisotropy in the R Fe X compounds originates mainly from a crystal "eld induced R anisotropy in which the second order crystal "eld parameter carries much weight. The present results show that the situation may be more complicated.…”

Magnetic ordering of Pr6Fe13Si and Nd6Fe13Au studied by neutron diffraction

“…In several investigations it was found that magnetic ordering is characterized by a Néel-type transition at temperatures around 400 K [9][10][11][12] which was also confirmed by Mössbauer spectroscopy [7,10]. The absence of a spontaneous magnetization of any significance at 4.2 K suggests that the magnetic structure consists of an antiferromagnetically ordered rare earth sublattice and an antiferromagnetically ordered Fe sublattice [9,11].…”

“…There are two rare earth sites, R 1 (8f) and R 2 (16l) and four Fe sites, Fe 1 (4d), Fe 2 (16k), Fe 3 (16l 1 ) and Fe 4 (16l 2 ). The magnetic properties of the R 6 Fe 13 X compounds were studied by numerous authors [2,[4][5][6][7][8][9][10][11][12].…”