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Two magnetic transitions at TM~160 K and at TM2~80-100 K, are observed in the magneto-superconducting RuEu2-xCexSr2Cu2O10-δ (TC = 32-50 K). Below TM2, the Ru5+ moments are weakly-ferromagnetically ordered and wide ferromagnetic hysteresis loops are observed, they become narrow and disappear at ~ 60-70 K. Dc magnetic studies on c-axis oriented epitaxial thin films of Ru-1222 on (100) SrTiO3 wafers show that the easy axis of the magnetization is in the basal plane and the Ru5+ ions are in their high-spin state. Above TM2, (i) small antiferromagnetic-like hysteresis loops reappear with a peak in the coercive fields around 120 K. (ii) A small peak at ~120 K is also observed in the dc and ac susceptibility curves. The two phenomena are absent in the non-superconducting RuEuCeSr2Cu2O10-δ (x=1) samples. Two scenarios are suggested for the phenomena at TM2M. (i) For x<1, the decrease of the Ce4+ content, is compensated by non-homogeneous oxygen depletion, which may induce a reduction of Ru5+ ions to Ru4+. The higher ordering temperature, TM, which does not change with x, may result from Ru4+ nano-size rich clusters, in which the Ru4+-Ru4+ exchange interactions are stronger than the Ru5+-Ru5+ interactions. Or alternatively,(ii) The presence of nanoparticles of a minor foreign extra Ru4+ magnetic phase, such as Sr-Cu-Ru-O3, in which Cu is distributed inhomogeneously in both the Ru and Sr sites.
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