Crystallographic and magnetic properties of Y3Fe5-xAlxO12

Al3+-substituted garnet Y3Fe5-xAlxO12 (x = 0-0, 0.25, 0.5, 0.75, and 1.0) was fabricated by a sol-gel method. The crystal structure Y3Fe5O12 is found to be a cubic with the lattice constant a(0) = 12.381+/-0.005 A. Mossbauer spectra of Y3Fe5-xAlxO12 were taken at various absorber temperatures ranging from 20 to 700 K. As the temperature increased toward T-N a systematic line broadening effect in the Mossbauer spectra was observed and interpreted to originate from different temperature dependencies of the magnetic hyperfine fields at various iron sites. It results from the distribution (C-6(n)) of Fe3+ and Al3+ at tetrahedral site. The isomer shifts indicated that the iron ions were ferric at the octahedral 16a site and the tetrahedral 24d sites. The quadrupole splitting showed that the orientation of the magnetic hyperfine field with respect to the principle axes of the electric field gradient was random. (C) 2002 Elsevier Science B.V. All rights reserved.