Influence of strontium on superconducting and magnetic properties of DyBa_2-xSr_xCu₃O_7-δ

The influence of substitution of Ba²⁺ with Sr²⁺ on the superconducting and magnetic properties of ceramic DyBa₂Cu₃O_7-δ samples with various oxygen contents has been investigated. The temperature and field dependences of magnetization and magnetic susceptibility of DyBa_2-xSr_xCu₃O_7-δ compounds with x=0, 0.5, and 1.0, were measured. The diamagnetic effect, the val ue of the intergrain critical field H_c1J, and the superconducting transition temperature T_c, were found to decrease while the intragrain critical field H_c1 and the width of the superconducting transition increased as the strontium content increased. The magnetic phase diagram H-T constructed for DyBa_1.5Sr_0.5Cu₃O_7-δ and DyBaSrCu₃O_7-δ compounds is topologically identical wit h the phase diagram of DyBa₂Cu₃O_7-δ where one H_c (T) line of the antiferromagnetic-paramagnetic transition in the magnetic field is seen. It was shown that the replacement of Ba²⁺ by Sr²⁺ leads to an enhancement of the low-dimensional properties. This is manifested by the appearance of a significant difference between the temperature of maximum χ (T), characterizing 2D magnetic correlations, and the Neel temperature, T_N, corresponding to a 3D ordering. In the DyBa_2-xSr_xCu₃O_7-δ system ther e is a structural phase transition with a heat absorption at the temperature of about 2.4 K.