Impact of Co and Mo substitution at Ru-site in RuSr2Eu1.5Ce0.5Cu2O10-δ magneto-superconductor

Substitution of both Co and Mo at Ru-site in RuSr2Eu1.5Ce0.5Cu2O10-delta system takes place iso-structurally in tetragonal structure (space group I4/mmm) with full solubility. The resistance versus temperature (R versus T) behavior of the pristine sample confirmed superconductivity (T-c(R=0)) around 25 K. The DC magnetization data (M versus T) for the same sample revealed magnetic transition (T-mag) at 140 K followed by superconducting transition (T-c(dia)) at 32 K. With progressive Co substitution at Ru-site both T-c(R=0) and T-c(dia) decrease monotonically and superconductivity is not observed for x >= 0.10 (10 at%). The magnetic behavior of 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 a clear antiferromagnetic transition at T-N = 31 K is observed regardless of Co content. In the case of Mo-doped ruthenocuprates Ru1-xMoxSr2Eu1.5Ce0.5Cu2O10-delta, it has been found that the magnetic transition temperature decreases with x. The samples of x = 0.8 and 1.0 are found to have no magnetic or superconducting effects. The values of the superconducting transition temperature obtained from the resistivity versus temperature data increase by 4.5 and 7.0 K for x = 0.2 and 0.4 respectively, and then decrease by 17 K for x = 0.6. The observed variation of T-c with x in case of Mo has been explained in terms of a theory which combines the effects of weakening magnetic behavior and reducing carrier concentration in a phenomenological manner.