FE-57 MOSSBAUER STUDIES OF BI2SR4FE3O12

Fe-57 Mossbauer and magnetization measurements of an iron compound Bi2 Sr4Fe3O12 isostructural with the high-T-c superconductor Bi2Sr2Ca2Cu3O 10, are made. Fe ions are found to be in the trivalent state from the Mossbauer isomer shift and the paramagnetic Curie constant. The Mossba uer spectra show a hyperfine magnetic spitting below 60 K. On the othe r hand, the temperature dependence of the magnetization has no anomaly at this temperature but has a broad maximum at 40 K, suggesting the o nset of magnetic order. The apparent disagreement of the magnetic tran sition of temperatures measured with the two methods can be ascribed t o the difference of the characteristic times of the measurements. The slowing down of the fluctuation of Fe3+ magnetic moments into the orde red phase seems to occur rather gradually in this oxide.