A MAGNETIC, NEUTRON-DIFFRACTION, AND MOSSBAUER SPECTRAL STUDY OF THE CE2FE17-XALX SOLID-SOLUTIONS

The magnetic properties of a series of Ce2Fe17-xAlx solid solutions wi th x equal to 0.00, 0.88, 2.06, 2.81, 3.98, 5.15, 6.08, 7.21, 8.20, 9. 08, 9.84, and 10.62 have been studied by magnetic measurements, neutro n diffraction, and Mossbauer spectroscopy. The compounds crystallize i n the rhombohedral Th2Zn17-type structure. Magnetization studies indic ate that the Curie temperature increases uniformly from 238 K for Ce2F e17 to 384 K for Ce2Fe14Al3 and then decreases at higher aluminum cont ent. Powder neutron diffraction results, obtained at 295 K, indicate t hat aluminum avoids the 9d site for all x values and preferentially oc cupies the 18h site at low aluminum content. Aluminum shows a marked p reference for the 6c site for x > 6. The room-temperature iron magneti c moments increase from x = 0 to 2 and then decrease for x > 2. The Mo ssbauer spectra have been fit with a binomial distribution of the near -neighbor environments in terms of a maximum hyperfine field, H-max, f or an iron with zero aluminum near neighbors, and a decremental field, Delta H, per aluminum near neighbor. The compositional dependence of the decremental field indicates the influence of aluminum on the long- range magnetic ordering in the compound. The compositional dependence of the weighted average maximum hyperfine fields and the weighted aver age isomer shifts in Ce2Fe17-xAlx may be understood in terms of a mixi ng of the 3d conduction band electrons with the 3p valence band electr ons of aluminum, a mixing which is more extensive than that associated with silicon in the Ce2Fe17-xSix solid solutions. We conclude that th is mixing has a larger influence on the magnetic properties of these s olid solutions than does the presence of a short iron-iron bond or the expansion or contraction of the lattice parameters and unit cell volu me. (C) 1996 American Institute of Physics.