A magnetic, neutron diffraction, and Mössbauer spectral study of the Nd2Fe17−xAlx solid solutions

Abstract

The magnetic properties of a series of Nd2Fe17−xAlx solid solutions, with x equal to 2.04, 4.01, 5.97, 7.94, and 9.06, have been studied by magnetic measurements, neutron diffraction, and Mössbauer spectroscopy. Magnetization studies indicate that the Curie temperature increases from 330 K in Nd2Fe17 to a maximum of ∼470 K at an x of 3.5. The compounds crystallize in the Th2Zn17 structure with lattice parameters and unit cell volumes which increase linearly with increasing aluminum content. The neutron diffraction results indicate that aluminum atoms are excluded from the 9d site, prefer the 18h site at low aluminum content, and prefer the 6c and 18f sites at high aluminum content. At 10 K the magnetic moments of the iron and neodymium atoms are collinear and take up a basal orientation at all aluminum contents. The moments decrease with increasing aluminum content and the magnetic moments per unit cell at 10 K are in excellent agreement with the 4.2 K saturation magnetization values. At 295 K the Nd2Fe17−xAlx solid solutions for x equal to 7.94 and 9.06 are paramagnetic. The magnetic Mössbauer spectra have been fit with a binomial distribution of the near-neighbor environments. The weighted average isomer shift increases, as expected, with increasing aluminum content as a result of interatomic charge transfer and intraatomic iron 4s–3d charge redistribution. The weighted average maximum hyperfine field at 295 K shows a maximum of 221 kOe at x equal to 2.04 but at 85 K it decreases uniformly with increasing aluminum content. The weighted average decremental field, ΔH, the change in the hyperfine field per aluminum near-neighbor, decreases with increasing aluminum content. It is proposed that, as a consequence of the increase in the average distance between an iron atom and its next near-neighbor shell with increasing aluminum content, the wavelength of the Friedel oscillation increases and the ratio of this wavelength and the shell distance becomes more favorable for ferromagnetic exchange.

Structural and Magnetic Properties of Sm2Fe17?xMnxNy with 0 ? x ? 6 and y ? 3

“…It can be seen that the lattice constants have a minimum at x 2. This behaviour is similar to the results obtained in Nd 2 Fe 17±x Mn x by Long et al[6].The thermomagnetic analysis of Sm 2 Fe 17±x Mn x compounds shows a typical ferromagnetic behaviour. The Curie temperature decreases from 393 K for x 0 to 130 K for x 6.…”

Magnetic and Mössbauer spectral study of ErFe11Ti and ErFe11TiH

“…In order to both build in constraints into the model and reduce the number of adjustable parameters, we assume that the three hyperfine parameters for each crystallographically inequivalent iron site vary linearly with the number, n, of titanium near neighbors, as given by for one additional titanium near neighbor. A similar linear dependence of the hyperfine field on the number of substitutional near-neighbor atoms has been successfully used [33][34][35][36] in the analysis of the Mössbauer spectra of the R 2 Fe 17Ϫx M x solid solutions. Hence, above the spin-reorientation temperature, the Mössbauer spectra of ErFe 11 Ti and ErFe 11 TiH are fit with nine sextets, which involve 18 hyperfine parameters, one linewidth, and one total absorption area.…”

Structure and magnetic properties of Nd2Co17−xGax compounds studied by magnetic measurements and neutron diffraction

“…In several previous investigations [9][10][11][12][13], neutron powder diffraction was used to study the site occupation of the non-magnetic elements M in rare earth compounds of the type R Fe \V M V (M"Al, Ga and Si). In all examples studied, quite substantial deviations from a statistical site distribution of the non-magnetic atoms over the four available Fe sites (6c, 9d, 18f and 18h) were observed.…”