Oxygen-deficiency effect on properties for the ordered-perovskite cuprate, Sr2Cu(Re0.69Ca0.31)Oy (y=6.0−5.4)

We have studied physical properties and crystal structures for oxygen-deficient phases of the cubic ordered-perovskite cuprate, Sr2Cu(Re0.69Ca0.31)Oy (y=6.0−5.4). It was found that the magnetic state undergoes phase transition from ferrimagnetic long-range order for y⩾5.9 to paramagnetism for y⩽5.7 via re-entrant-type spin-glass randomness in the narrow composition range around y∼5.8, as the oxygen content y decreases. The electrical resistivity becomes insulated, and the lattice constant expands simultaneously with decrease in y. The abrupt suppression of the ferrimagnetic state was observed in the oxygen-deficiency phase around 5.9⩾y⩾5.7. This is presumably attributed to microscopic phase separation accompanied by the partial cut-off of the Cu-O-Cu antiferromagnetic correlation path, which is caused by cation disorder and reduction of the oxidation state of the cations.