Multiple magnetic ordering temperatures in RuSr2Eu1.5Ce0.5Cu2O10-δ system

We report synthesis and magnetic characterization of variously processed magneto-superconducting (Rutheno-cuprates) RuSr2Eu1.5Ce0.5Cu2O10-delta . The compound crystallizes in I4/mmm tetragonal structure. Magnetization measurements showed bulk magnetic ordering and superconductivity at around 100 K and 30 K, respectively. Further, the careful examination of the low field magnetic susceptibility reveals two minor magnetic transitions at around 135 K and 200 K, in addition to the major transition at 100 K. When the samples are processed in different environments of air, O-2 and slightly pressurized O-2, the nature of magnetic transitions and the superconductivity changes dramatically. The highest superconducting transition is achieved for the high pressure O-2 annealed samples and the lowest for the air annealed one. On the other hand, the minor magnetic transitions are more prominent in air-annealed samples. Though the minor magnetic transitions are intrinsic to all variously processed samples, they are not clearly seen for higher O-2 content samples. Basically, the Ru spins order antiferro magnetically at around 200 K (first minor transition), and reorients themselves at 125 K (second minor transition) before finally ordering in canted ferromagnetic state or a spin glass structure. These results can be explained on the basis of fluctuating valance of Ru4+/Ru5+.