Mossbauer spectroscopy study on the effect of Al-Cr co-substitution in yttrium and yttrium-gadolinium iron garnets

Room-temperature Mossbauer spectra were recorded for two series of Al-Cr co-substituted rare-earth iron garnets: YIG (Y3AlxCrxFe5-2xO12) and Y-GdIG (Y(1.)5Gd(1.5)Al(x)Cr(x)Fe(5-2x)O(12)). All the spectra were fitted with two magnetic sextets, one sextet corresponds to the (a) octahedral site and the other corresponds to the (d) tetrahedral site. The hyperfine fields for all the samples show a reduction of (similar to5 Tesla) per substituted atom with increasing x. The values of the hyperfine fields of the Y-GdIG samples are slightly higher than those of the YIG samples. The relative intensities of the two sextets show that upon substitution, the Al-Cr occupy the (a) site rather than the (d) site. Also, the line widths of the two sextets were found to increase systematically upon substitution, due to the increasing atomic disorder as the Al-Cr contents increase.