A magnetic and Mossbauer spectral study of the Tb2Fe17-xAlx solid solutions

The magnetic properties of a series of Tb2Fe17-xAlx solid solutions, with x equal to 0.00, 1.00, 1.98, 3.14, 4.08, 5.10, 6.06, 7.16, and 8.12, have been studied by magnetic measurements and Mossbauer spectroscopy. Magnetization studies indicate that the Curie temperature increases from 420 K in Tb2Fe17 to a maximum of 475 K in Tb2Fe13.86Al3.14. The magnetization results indicate an antiferromagnetic coupling of the terbium sublattice with the iron sublattice at low temperature. The magnetically ordered Mossbauer spectra have been fit with a binomial distribution of near neigbors. The weighted average maximum hyperfine field, H-max, decreases by 12 kOe per aluminum at 85 K. The decrease in hyperfine field is due to the dilution of the magnetic moments by aluminum. The weighted average decremental field, Delta H, decreases by 2 and 1 kOe per aluminum at 85 and 295 K, respectively. The compositional dependence of the decremental field indicates the presence of RKKY type spatial spin oscillation in the 4s conduction band, an oscillation which is modified by the presence of aluminum, The weighted average isomer shift increases by 0.016 and 0.010 mm/s per aluminum at 85 and 295 K, respectively, because of both the screening of the 4s electrons by the 3d electrons due to interband mixing of the 3d band with the valence band of aluminum, and the unit cell volume expansion upon aluminum substitution.