Crossing point phenomena (T* = 2.7 K) in specific heat curves of superconducting ferromagnets RuSr2Gd1.4Ce0.6Cu2O10-δ

Abstract

Crossing point phenomena are one of the interesting and still puzzling effects in strongly correlated electron systems. We have synthesized RuSr2Gd1.4Ce0.6Cu2O10-δ (GdRu-1222) magneto-superconductor through the standard solid state reaction route and measured its magnetic, transport, and thermal properties. We also synthesized RuSr2Eu1.4Ce0.6Cu2O10-δ (EuRu-1222) then measured its heat capacity in zero magnetic fields for reference. The studied compounds crystallized in the tetragonal structure with space group I4/mmm. To explore the crossing point phenomena, the specific heat [Cp (T)] was investigated in the temperature range 1.9-250 K, under magnetic field of up to 70 kOe. Unfortunately though no magnetic and superconducting transitions are observed in specific heat, a Schottky-type anomaly is observed at low temperatures below 20 K. This low temperature Schottky-type anomaly can be attributed to splitting of the ground state spectroscopic term 8S7/2 of paramagnetic Gd3 + ions by both internal and external magnetic fields. It was also observed that Cp (T) is measured for different values of magnetic field, possesses the same crossing point (T* = 2.7 K), up to the applied magnetic field 70 kOe. A quantitative explanation of this phenomenon, based on its shape and temperature dependence of the associated generalized heat capacity (Cp), is presented.