A Magnetic, Neutron Diffraction, and Mössbauer Spectral Study of the Ce₂Fe₁₇₋ₓGaₓ Solid Solutions

The magnetic properties of the rhombohedral Ce2Fe17-xGax solid solutions, with x equal to 0.3, 0.5, 0.7, 1.0, and 2.0, have been studied by magnetic measurements, neutron diffraction, and Mössbauer spectroscopy. Magnetization studies indicate that, as the unit cell volume expands with Ga addition, the Curie temperature increases from 238 K for Ce2Fe17 to 406 K for Ce2Fe15Ga2. Powder neutron diffraction measurements at 295 and 14 K indicate that the Fe moments are both oriented in the basal plane and increase with increasing Ga content. The Mössbauer spectra, which have been fit with a binomial distribution of the near-neighbor environments, indicate that the maximum, hyperfine field, Hmax, increases with increasing Ga content and is largest for the 6c site. The decremental field, ΔH, per added Ga atom is virtually independent of temperature and Ga content, indicating that the next-nearest-neighbor interactions are very small. The compositional dependence of the isomer shifts for R2Fe17-xMx, where R is Ce or Tb and M is Al, Si, or Ga, is analyzed in terms of volume and chemical terms, the second of which reveals the importance of the electronic configuration of M in understanding its influence on the magnetic properties of these solid solutions. Finally, the similarities and differences in the changes in crystallographic, magnetic, and Mössbauer spectral properties of R2Fe17-xMx, at low x values, indicate that electronic rather than structural factors are more important in modifying the magnetic properties and indicate the need for extensive band structure calculations on these solid solutions