Annealing effect on crystal structure, carrier concentration, and magnetism inone-layer hole-doped T*-type cuprates Pr1.6Sr0.4CuO4−δ

We investigated the effect of annealing on the crystal structure, effective hole concentration, and magnetic properties of T*-type cuprates Pr_1.6Sr_0.4CuO_4−δ (PSCO) using neutron powder diffraction, X-ray absorption spectroscopy, and muon spin rotation. A significant number of oxygen vacancies were observed at both the apical and in-plane oxygen sites in the Ar-annealed (Ar-AN), as-sintered (AS), and high-pressure O₂-annealed (O₂-AN) PSCO compounds. Our experiments reveal a noticeable reduction in the effective hole concentration, shifting from the heavily-doped to lightly-doped region. Furthermore, we observed enhanced static magnetic order in Ar-AN compound, whereas the transition temperature was suppressed in the AS and high-pressure O₂-AN PSCO. The present results demonstrate an exceptional example of lightly-doped T*-type cuprates. In particular, apical oxygen is more sensitive and substantially influenced by annealing, and the enhanced magnetism in reduction annealing reduces the effect of in-plane oxygen scenario under annealing.