Indication of high local fields in the $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_{2.9375}{\mathrm{Fe}}_{0.0625}{\mathrm{O}}_{\delta }$ superconductor by Mössbauer spectroscopy

Mössbauer spectra of a $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_{2.9375}{\mathrm{Fe}}_{0.0625}{\mathrm{O}}_{\delta }$ superconducting sample were obtained at different temperatures ranging from 50 to 120 K. The results clearly show that Fe substitutes for Cu in this complex. All the spectra showed a pair of superimposed quadrupole doublets with essentially the same splittings but different isomer shifts, corresponding to two different environments of the substituted atoms. The values of the isomer shifts obtained correspond to low-spin Fe atoms, which implies strong local fields, or strong bonding between the atoms.