Magnetic transition and Meissner shielding in ferromagnetic high-Tc superconductor RuSr2Gd1.4Ce0.6Cu2O10-δ

The magnetic superconductor RuSr2Gd1.4Ce0.6Cu2O10-δ was studied by means of detailed magnetization measurements in order to clarify its complex magnetic and superconducting properties. Our experiments agree with a model indicating that the in-plane component of the Ru moment might transform from a spin-glass ground state to a ferromagnetically coupled excited state by application of a small magnetic field below the magnetic transition temperature. The experiments also show that a full Meissner state is present at the low temperature, the low magnetic field region of the phase diagram. This is in contrast to the previous prediction that no Meissner state exists in this material for an internal magnetic field of several hundred Oersteds in the CuO2 planes exerted by the Ru sublattice and exceeding the lower critical field.