FE ENVIRONMENTS AND MAGNETIC ORDER IN YSR2CU2FEO7.26

Fe-57 Mossbauer absorption spectroscopy and magnetic susceptibility measurements of YSr2Cu2FeO7.26 have been performed in order to further elucidate the Fe environments and magnetic ordering temperatures al high doping levels in the YBa2Cu3O7 structure. We find Fe3+ in three environments. Fe substitutes in the Cu(1) chain sites in 5-fold and 6-fold coordination, and in the Cu(2) plane sites in 5-fold coordination. The onset of magnetic ordering is near 65 K. This latter result is much lower than expected given the high Fe content and 5-fold and 6-fold coordination, which trap hotes in the Cu(1)Oy planes. We interpret the lower magnetic ordering temperature to be due to more efficient transfer of available untrapped holes from the Cu(1)Oy planes to the Cu(2)O2 sheets.