Low-temperature behavior of specific heat curves in ruthenocuprate RuSr₂Gd_1.5Ge_0.5Cu₂O _{10 - δ}: Superconducting, magnetic and crossing-point effects

Magnetic and superconducting properties of polycrystalline samples of RuSr₂Gd_1.5Ce_0.5Cu₂O _{(10 - δ)}, asprepared (by solid-state reaction) and annealed in pure oxygen at different pressure 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 ≈ 37.5 K) and a Schottky-type anomaly below 20 K. It is found that curves C(T) taken for different values of magnetic field have the same crossing point (at T _* ≈ 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 _* ≈ 3.7 T. These effects are manifestations of the crossing-point phenomenon, which is supposed to be inherent for strongly correlated electron systems.