Mössbauer studies of Fe1−xMxBO3 (x = 0, 0.1; M = Al3+, Ga3+, Cr3+) close to the Tc

The results of a Mossbauer study on the effect of substitution of Al3+, Ga3+, and Cr3+ in ferromagnetic FeBO3 close to the Tc are presented. The Curie temperatures of FeBO3, Fe0.9Al0.1BO3, Fe0.9Ga0.1BO3, and Fe0.9Cr0.1BO3 have been determined to be 352, 317, 319, and 335 K, respectively. “Anomalous” spectra have been found to appear just 1° below the Tc for FeBO3, but 15° below the Tc for substituted borates. The inadequacy of static models in explaining these spectra has been pointed out. These spectra have been simulated using relaxation models and estimates of activation energy obtained for spin-flip processes. The results are attributed to dominant superparamagnetic relaxation effects due to the presence of clusters. Mossbauer spectra of FeBO3 substituted by a magnetic ion, viz., Cr3+, are found to differ significantly from those of the above-mentioned samples.