A magnetic, neutron diffraction, and Mössbauer spectral study of Nd2Fe15Ga2 and the Tb2Fe17−xGax solid solutions

Abstract

An x-ray diffraction study of the substitution of gallium in Tb2Fe17 to form the Tb2Fe17−xGax solid solutions indicates that the compounds adopt the rhombohedral Th2Zn17 structure. The unit cell volume and the a-axis lattice parameter increase linearly with increasing gallium content. The c-axis lattice parameter increases linearly from x=0 to 6 and then decreases between x=7 and 8. Magnetic studies show the Curie temperature increases by ∼150° above that of Tb2Fe17 to reach a maximum between x=3 and 4, and then decreases with further increases in x. Neutron diffraction studies of Nd2Fe15Ga2 and Tb2Fe17−xGax, with x equal to 5, 6, and 8, indicate that the gallium completely avoids the 9d site, occupies the 6c ‘‘dumbell’’ site only at high values of x and strongly prefers the 18f site at high values of x. The magnetic neutron scattering indicates both that the terbium sublattice magnetization couples antiferromagnetically with the iron sublattice and that there is a change in easy magnetization direction from planar to axial with increasing gallium concentration. This change in easy magnetization direction is explained in terms of a sign reversal of the second-order crystal field parameter, A02, the most important parameter responsible for determining the terbium sublattice anisotropy. The Mössbauer effect spectra indicate a larger room-temperature average hyperfine field at the iron site in the Tb2Fe17−xGax solid solutions than in several related R2Fe17 compounds. The large observed increase in the isomer shift with increasing gallium content results from interatomic charge transfer and intraatomic s-d charge redistribution in the presence of gallium.

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.…”

Effect of Substitution of Iron by Cobalt on the Physical Properties in the Sm2Fe14Mn3 Compound

“…There are two ways to improve the magnetic properties of R 2 Fe 17 compounds. The first one is a partial substitution of iron by a metal or a metalloid [2][3][4][5][6] or a partial substitution of the rare earth element [7,8]. The second method is by interstitial modification of nitrogenation or carbon [9].…”

The effects of the combined substitution of Y and Ga on the crystallographic structure of Nd2−xYxFe17−yGay intermetallic compounds

“…Permanent magnets must possess higher magnetization, higher anisotropy and higher Curie temperature (T c ). Extensive studies in the past years show that the magnetic properties of R 2 Fe 17 can be improved by the incorporation of interstitial atoms [5,6], the substitution of suitable elements for Fe [7][8][9][10], the substitution of different rare earth [11] or the combination of several techniques [12][13][14][15][16][17]. Although, the reasons are not very sound, the improvements of the magnetic properties are closely related to the elimination of some bond lengths unfavorable to the ferromagnetic exchange.…”