Experimental study of magneto-superconductor RuSr2Eu1.5Ce0.5Cu2O10-δ:: peculiar effect of Co doping on complex magnetism and Tc variation

We report structural, electrical, thermopower and magnetic properties of the Ru1-xCoxSr2Eu1.5Ce0.5Cu2O10-delta (1.0 >= x >= 0.0) system. Substitution of Co at the Ru site in the Ru1-xCoxSr2Eu1.5Ce0.5Cu2O10-delta system takes place iso-structurally in the tetragonal structure (space group I4/mmm) with full solubility (x = 1.0). Superconductivity (SC) exists for x up to x = 0.075 only and at higher Co concentrations SC is totally suppressed. The magnetic behaviour of the materials with Co up to x = 0.2 preserves the magnetic structure of the parent RuSr2Eu1.5Ce0.5Cu2O10-delta compound. For 0.8 >= x >= 0.2 an antiferromagnetic-like transition is seen at T-N = 31 K, which remains invariant regardless of the Co content. CoSr2Eu1.5Ce0.5Cu2O10-delta (x = 1) seems to be an itinerant magnet, which orders magnetically at around 110 K, though for such an assertion further work is warranted. In general, the magnetization measurements as such did not reveal the complete information on the magnetic structure and hence the neutron scattering measurements are still required to resolve the complex magnetism of Ru1-xCoxSr2Eu1.5Ce0.5Cu2O10-delta and even the pristine system.