Transport, thermal and magnetic properties of RuSr_2(Gd_{1.5}Ce_{0.5})Cu_2O_{10-\delta}, a magnetic superconductor

Resistivity, thermoelectric power, heat capacity and magnetization for samples of RuSr_2(Gd_{1.5}Ce_{0.5})Cu_{2}O_{10-\delta} were investigated in the temperature range 1.8-300 K with a magnetic field up to 8 T. The resistive transitions to the superconducting state are found to be determined by the inhomogeneous (granular) structure, characterized by the intragranular, T_{c0}, and intergranular, T_{cg}, transition temperatures. Heat capacity, C(T), shows a jump at the superconducting transition temperature T_{c0}\approx 37.5 K. A Schottky-like anomaly is found in C(T) below 20 K. This low temperature anomaly can be attributed to splitting of the ground term $^{8}S_{7/2}$ of paramagnetic Gd^{3+} ions by internal and external magnetic fields.Comment: 3 pages (4 figs. incl.), reported at 50th Magnetism and Magnetic Materials Conference, San Jose, CA, USA, 200

Characteristic crossing point (T∗≈2.7T_{\ast}\approx 2.7 K) in specific-heat curves of samples RuSr2_2Gd1.5_{1.5}Ce0.5_{0.5}Cu2_2O10−δ_{10-\delta} taken for different values of magnetic field

Magnetic properties of polycrystalline samples of RuSr$_2$(Gd$_{1.5}$Ce$_{0.5}$)Cu$_{2}$O$_{10-\delta}$, as-prepared (by solid-state reaction) and annealed (12 hours at 845$^{\circ}$C) in pure oxygen at different pressure (30, 62 and 78 atm) are presented. Specific heat and magnetization were investigated in the temperature range 1.8--300 K with a magnetic field up to 8 T. Specific heat, $C(T)$, shows a jump at the superconducting transition (with onset at $T\approx 37.5$ K). Below 20 K, a Schottky-type anomaly becomes apparent in $C(T)$. This low-temperature anomaly can be attributed to splitting of the ground term ${^8}S_{7/2}$ of paramagnetic Gd$^{3+}$ ions by internal and external magnetic fields. It is found that curves $C(T)$ taken for different values of magnetic field have the same crossing point (at $T_{\ast}\approx 2.7$ K) for all samples studied. At the same time, $C(H)$ curves taken for different temperatures have a crossing point at a characteristic field $H_{\ast}\approx 3.7$ T. These effects can be considered as manifestation of the crossing-point phenomenon which is supposed to be inherent for strongly correlated electron systems.Comment: 10 pages, 7 figures, submitted to J. Phys.: Condens. Matte