The effect of oxygen content on the magnetic and transport properties of FeSr2Y1.5Ce0.5Cu2O8+x

The magnetic and transport properties of FeSr2Y1.5Ce0.5Cu2O8+x have been studied in the oxygen saturated (OS) and oxygen reduced (OR) states. We find that the low temperature spin-glass transition is not affected by the oxygen content in the SrFeO3−x subunit although the magnitude of the Curie–Weiss temperature is significantly larger in the OR sample. The oxygen reduced sample also has an antiferromagnetic transition at ~310 K that is likely to be due to antiferromagnetic ordering of the Cu moments in the CuO2 plane. The resistivity from the OR sample can be modeled in terms of variable range hopping and activated conduction, which indicates that it is a very disordered semiconductor. The oxygen saturated sample has additional holes in the CuO2 plane and the absence of superconductivity is likely due to pair breaking from Fe on the Cu sites in the CuO2 plane. We modeled the resistivity in the OS state in terms of inhomogeneous transport where there are metallic regions and disordered regions that have a resistivity with a 1/Tm temperature dependence at low temperatures.