Protected Vacuum Annealing Effect on Single Crystals of Pr_1-xLaCe _x CuO₄ in the Overdoped Regime

We report the effect of protected vacuum annealing on the superconducting (SC) and magnetic properties of Pr_1-xLaCe _x CuO₄ (PLCCO) single crystals in the overdoped regime (x = 0.13 - 0.20). The powders and single crystals of PLCCO with all x were synthesized by the solid state reaction and grown by the travelling solvent floating zone (TSFZ) method, respectively. The powder x-ray diffraction (XRD) results analyzed by the Rietveld method have shown that there is a systematic decrease in the c-axis length with increasing x, suggesting the proper substitution of Ce for Pr in overdoped PLCCO up to x = 0.20. The so-called two-step annealing performed in the overdoped regime was essential for increasing the SC volume fraction estimated from the magnetic susceptibility measurements. Furthermore, the temperature dependence of the normal-state magnetic susceptibility for reduced crystals of PLCCO with all x has exhibited a Curie-Weiss-like behavior regardless of various steps of the protected vacuum annealing process.