EVALUATION OF THE LOW-TEMPERATURE MOSSBAUER-SPECTRA OF YBA2(CU0.9FE0.1)(3)O-6.9 BY MEANS OF A FIELD DISTRIBUTION MODEL

Fe-57 Mossbauer spectra of YBa2(Cu0.9Fe0.1)(3)O-6.9 measured at low te mperatures show spontaneous magnetic ordering combined with broad reso nance lines. It is shown that these spectra can be well understood ass uming an asymmetric distribution of the absolute values of the magneti c field at the nucleus. For the fitting procedure, we used the full Ha miltonian for combined electric and magnetic static hyperfine interact ion. The number of free parameters for the fits was restricted as much as possible. For the iron sites A and B (Cu(1) sites), the ordering t emperature is 26.5 K, for the iron site C (Cu(2) site), it is 31 K. Th e mean saturation hyperfine magnetic field is different for the differ ent iron sites (26 T for the A site, 20 T for the B site and 43.5 T fo r the C site). Using these fit results and our results on thin films, we can give a consistent interpretation of the Mossbauer spectra of YB a2(Cu1-xFex)(3)O-7-delta.