Effect of Nearest Neighbor Ions on the Hyperfine Fields at 57Fe Nuclei in TbFe1-xCrxO3

Mössbauer experiment has been performed in TbFe 1- x Cr x O 3 . Hyperfine field at 57 Fe nuclei is 550 kOe at 0 K for x =0, and it decreases by 9 kOe when one Fe 3+ ion is replaced by a Cr 3+ ion at the nearest neighbor site of 57 Fe 3+ ion. This decrease is attributed to the change in the supertransferred hyperfine interaction caused by the replacement. Temperature dependence of the hyperfine field is explained by a modified molecular field theory for various concentrations. In the Cr 3+ concentration higher than x =0.8, anomalous increase is observed in the hyperfine field. The anomaly arises from the concentration dependence of the zero-point spin reduction at 57 Fe. The positive superexchange coupling of Fe 3+ –O–Cr 3+ gives a reasonable explanation on the magnitude of the anomaly.