Mossbauer studies of Y3Fe5-xAlxO12 nanopowders prepared by mechanochemical method

A series of Al substituted yttrium iron garnet (Al-YIG) nanopowders with nominal formula of Y3Fe5-xAlxO12 which x varied in steps of 0.0, 0.5, 1.0, 1.5 and 2.0 were prepared via mechanochemical processing. The samples were milled for 40 h in a high energy planetary mill and then calcined at different temperatures from 1,300 to 1,100 degrees C. X-ray diffraction patterns reveal that the structure of nanopowders are bcc and the garnet phase has been obtained after calcining. The average crystallite sizes are in the range of 24-45 nm, using Scherrer's formula. The lattice constant of the samples decreases by increasing Al concentration. To investigate the site preference of Al3+ ions, room temperature Fe-57 Mossbauer spectra for the samples were recorded and analyzed. The hyperfine field values for octahedral and tetrahedral sites of the samples decrease by increasing x value. This decrease in magnetic hyperfine field reflects a reduction of the superexchange interaction by the progressive substitution of Al for Fe, which is also evident in the behavior of the magnetization and T-C for the samples.