TIME-DIFFERENTIAL PERTURBED-ANGULAR-CORRELATION AND EMISSION MOSSBAUER STUDIES ON RU-99 ARISING FROM RH-99 IN FE3O4

Hyperfine interactions at Ru-99(<-- Rh-99) nuclei dilutely incorporated into Fe3O4 were studied by means of two techniques: time-differential perturbed-angular correlation (TDPAC) and emission Mossbauer spectroscopy. The former measurements were performed in the temperature range between 10 and 885 K, and the latter at 5 K. The value of the hyperfine magnetic field (H(hf)) at 10 K obtained by the TDPAC measurement is -160 kOe, the absolute value of which is essentially in agreement with that derived from the Mossbauer spectrum at 5 K, 145 kOe. The negative sign of H(hf) means that Ru-99 ions are located at the octahedral (B) sites. The temperature dependence of H(hf) obtained by the TDPAC measurements suggests that there are two origins for the observed H(hf): the major part of H(hf) (about -135 kOe at 10 K) is produced by the magnetic moments of Fe3+ at the nearest-neighbor tetrahedral (A) sites via the A-O-B supertransfer mechanism, and the minor one (about -25 kOe at 10 K) by that of the unpaired 4d electron of the Ru-99 ion itself. The isomer shift obtained by the emission Mossbuer measurement and the temperature dependence of H(hf) indicate that the average valence of a Ru ion is larger than +2 but smaller than +3. Such a low valence is not common in ruthenium oxides. The estimated value of the supertransferred hyperfine magnetic field at Ru-99 in Fe3O4 is compared with those at Fe-57 and Sn-119 in the same matrix.