Mössbauer spectral invetigations of ultrafine rare-earth iron garnets

Abstract

Ultrafine rare-earth iron garnets (RIG) in the crystalline size range 1.0–35 nm, prepared by the citrate precursor method have been investigated by Mossbauer spectroscopy at room temperature. The crystallites of 10–35 nm size show two six-line spectra corresponding to tetrahedral and octahedral Fe3+ with isomer shifts, δ, and magnetic hyperfine fields, H hf, comparable to the bulk polycrystalline garnets. However, 1.0–1.5 nm crystallites (X-ray amorphous) show a quadrupole split doublet due to superparamagnetic nature with isomer shifts (0.3 mms−1) internediate between tetrahedral and octahedral values of bulk garnets. The relative increase of tetrahedral δ and the decrease in the octahedral δ indicate, respectively, an increase of tetrahedral Fe-O bond distance and a decrease of octahedral Fe-O bond distance in the ultrafine state, in complete agreement with the observations made earlier in the spectrochemical investigations. The lines are broad (linewidth=0.65 mms−1) and the quadrupole splittings are relatively larger (ΔE Q = 1.0 mms−1) indicating large deviation from cubic symmetry at the Fe3+ sites.