Structural properties of (Nd_0.33Eu_0.2Gd_0.47)Ba₂Cu₃O_y studied by magnetic and infrared measurements

Reflectance of a single crystal of the (Nd_0.33Eu_0.2Gd_0.47)Ba₂Cu₃O_y superconductor was measured as a function of frequency from 35 to 8000 cm⁻¹ and for temperatures from 10 to 300 K. The Kramers-Kronig analysis with appropriate extrapolations was used to calculate response functions. The AC conductivity displays phonons at frequencies typical for the whole family of REBa₂Cu₃O_y cuprates. The Drude term is rather low in comparison to optimally doped cuprates. The spectra were fitted to study temperature dependence of their parameters. DC electrical conductivity and magnetization were measured using a four-probe technique and a vibrating sample magnetometer, respectively. The remnant J_c reached 21.0 kA/cm², J_c at the secondary peak was 20.0 kA/cm² at 2.0 T.