A study of several rare-earth transition metal intermetallic compounds.

摘要

A series of {dollar}rm Rsb2Fesb{lcub}17-x{rcub}Msb{lcub}x{rcub}{dollar} solid solutions, where R is cerium, neodymium, or terbium, and M is a non-magnetic atom, namely aluminum, gallium, or silicon, have been studied by Mossbauer spectroscopy, neutron diffraction, and magnetization measurements.; The analysis of the Mossbauer spectra at 85 K of the {dollar}rm Rsb2Fesb{lcub}17-x{rcub}Msb{lcub}x{rcub}{dollar} compounds reveals that the iron hyperfine fields decrease with the non-magnetic atom substitution for iron in the unit cell, a decrease attributed to the reduction in the total magnetization. The decremental hyperfine fields reveal the presence of a long range RKKY-type interaction, an interaction mainly carried to the iron atoms via 4s conduction electrons. The compositional dependence of the isomer shifts may be understood in terms of the changes in the site volumes and the screening of the s electrons at the iron nucleus.; Neutron diffraction studies of the {dollar}rm Rsb2Fesb{lcub}17-x{rcub}Msb{lcub}x{rcub}{dollar} solid solutions reveal that the substitutional non-magnetic atoms prefer the 18h site, a site which has the largest number of near-neighbor rare-earth atoms. This preference results from the electronegativity difference between the rare-earth atoms and the substitutional atoms. The compositional dependence of the lattice parameters of the {dollar}rm Rsb2Fesb{lcub}17-x{rcub}Msb{lcub}x{rcub}{dollar} solid solutions indicates that aluminum and gallium increase the unit cell volume, whereas silicon decreases the unit cell volume. Magnetic neutron diffraction studies of the {dollar}rm Rsb2Fesb{lcub}17-x{rcub}Msb{lcub}x{rcub}{dollar} solid solutions indicate that the magnetic moments of iron are sensitive to the changes in the site volumes.; Magnetic measurements show an increase in the Curie temperatures of the {dollar}rm Rsb2Fesb{lcub}17-x{rcub}Msb{lcub}x{rcub}{dollar} solid solutions upon substitution of aluminum, silicon, and gallium in the unit cell. The increase in the Curie temperatures is attributed to the overall enhancement of the positive exchange interactions between all iron atoms upon substitution of non-magnetic atoms in the unit cell. The maximum Curie temperatures of the {dollar}rm Rsb2Fesb{lcub}17-x{rcub}Msb{lcub}x{rcub}{dollar} solid solutions are observed for x values between three and four. A mean field analysis of the Curie temperatures and the saturation magnetizations of the {dollar}rm Rsb2Fesb{lcub}17-x{rcub}Msb{lcub}x{rcub}{dollar} solid solutions indicates an increase in the strength of the positive exchange coupling between iron atoms for x values up to four.