Layered (Cu,Fe) oxides of double perovskite structure: Correlation between structural and magnetic-property changes in BaY(Cu0.5Fe0.5)2O5+δ upon high-pressure heat treatment

Abstract

In this paper, we report the correlation between the magnetic property and the local structure in BaY(Cu0.5Fe0.5)2O5+δ of the “0112” phase containing an unusually large amount of excess oxygen, δ of ∼0.2, when heat treated under a high pressure of 5 GPa. Magnetic susceptibility measurements showed that upon the high-pressure heat treatment, the lower-temperature magnetic transition which had been observed in normal-pressure synthesized, antiferromagnetic BaY(Cu0.5Fe0.5)2O5 disappeared and the higher-temperature transition, i.e., the Néel temperature, was lowered. According to a Rietveld analysis based 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 Mössbauer spectroscopy measurements strongly suggested the existence of excess oxygen in the yttrium plane.