LAYERED (CU,FE) OXIDES OF DOUBLE PEROVSKITE STRUCTURE - CORRELATION BETWEEN STRUCTURAL AND MAGNETIC-PROPERTY CHANGES IN BAY(CU0.5FE0.5)(2)O5-PRESSURE HEAT-TREATMENT(DELTA UPON HIGH)

In this paper, we report the correlation between the magnetic property and the local structure in BaY(Cu0.5Fe0.5)(2)O5+delta of the ''0112'' phase containing an unusually large amount of excess oxygen, delta of similar to 0.2, when heat treated under a high pressure of 5 GPa. Mag netic susceptibility measurements showed that upon the high-pressure h eat treatment, the lower-temperature magnetic transition which had bee n observed in normal-pressure synthesized, antiferromagnetic BaY(Cu0.5 Fe0.5)(2)O-5 disappeared and the higher-temperature transition, i.e., the Neel temperature, was lowered. According to a Rietveld analysis ba sed on x-ray-diffraction data and space group P4/mmm, the distinction between Cu and Fe positions along the c axis inside the oxygen pyramid disappeared. Coulometric titrations and Mossbauer spectroscopy measur ements strongly suggested the existence of excess oxygen in the yttriu m plane.