Mössbauer and Magnetization Study of YBa₂(Cu_1−xFe_x)₃O_∼6.9

Abstract

Mössbauer spectra of ⁵⁷Fe in YBa₂(Cu_1−xFe_x)₃O_y were studied for the samples keeping the oxygen concentration constant, y=6.87±0.05. Using the results of EXAFS measurement, we find that changes in the Mössbauer pattern with iron concentration can be explained from changes in the oxygen coordination around iron. The number of iron atoms with an octahedral coordination increases rapidly with a change in the crystal structure from orthorhombic to tetragonal. This increase has a close correlation with the decrease in a zero-field cooled magnetization in the superconducting state. These results are consistent with that the tetragonal structure observed by X-ray diffraction is induced by the increase of the number of octahedrally coordinated iron and consists of microdomains with the orthorhombic structure inside the domains.