Abstract
The 2212 and 4334 phases of Bi-based oxide superconductors have been studied mainly with respect to the 57Fe-probe Mössbauer effect using the substitution of Fe for Cu in them. Their Mössbauer spectra at room temperature are paramagnetic, while the spectra at 4.2 K without external magnetic field are composed of the paramagnetic doublet and magnetic component with a hyperfine field of about 40 T except for that of a sample containing 1 at%Fe. With an external field of 5 T the spectra of all samples at 4.2 K have only the magnetic component, suggesting that iron atoms at the Cu sites in the samples have a large magnetic moment of about 2.7 Bohr magneton. The appearance of the magnetic hyperfine structure of iron in the phases is probably due to the formation of antiferromagnetism in the CuO2 plane. On the other hand, the appearance of paramagnetic doublet at 4.2 K indicates the spins of iron atoms fluctuate faster than the life time of the 57Fe excited state(10−7 s) and is considered to be arising from the iron in the superconductive CuO2 plane.
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