Crystal Growth and Neutron Scattering Study of Spin Correlations of the T′-Structured Pr_2-xCa _x CuO₄

We studied Ca-doping effect on spin correlations in T′-structured cuprate oxide RE₂CuO₄ (RE: rear earth) with growing a sizable single crystal of Pr_2-xCa _x CuO₄ (x=0.05 and 0.10) as well as synthesizing powder samples of Pr_1.90Ca_0.10CuO₄ and Eu_1.90Ca_0.10CuO₄. In the all as-prepared and annealed samples, no evidence of shielding signal associated with superconductivity was observed by magnetic susceptibility measurement. Elastic neutron scattering measurements on the as-grown Pr_1.90Ca_0.10CuO₄ clarified the existence of long-ranged magnetic order with commensurate spin correlation. The ordering temperature was determined to be ∼290K, which is comparable to Néel temperature in the parent compound of Pr₂CuO₄. The existence of commensurate low-energy spin excitation was also confirmed by inelastic neutron scattering measurements for the annealed Pr_1.95Ca_0.05CuO₄. These results strongly suggest a negligible Ca-doping effect on the physical properties in T′-RE₂CuO₄, which is quite different from the drastic doping evolution of magnetism in T-RE₂CuO₄.