Decoupling of the Magnetic State in RuSr2Eu1.5Ce0.5Cu2O10-δ

Abstract

We have studied the effect of Zn substitution for Cu, on the superconducting (SC) and magnetic properties of RuSr 2 Eu 2-x Ce x( Cu 1-x Zn x)2 O 10 (Ru-1222) for x = 0, 0.01 and 0.025. Similar to all other Zn doped HTSC materials, Zn reduces TC, from TC = 38 to 26 K for x = 0 and 0.01 respectively. The system with x = 0.025 is not SC down to 4.2 K. On the other hand, the magnetic state of the Ru sublattice is not significantly affected by the presence or absence the SC State. Thus, the two states are practically decoupled. The wide ferromagnetic hysteresis loops which open at 5 K close themselves at elevated temperatures and the remanent magnetizations (Mrem) and the coercive fields (HC) become zero around Tirr = 80 K . Surprisingly, at Tirr < T < TM a reappearance of the Mrem and HC (with a peak at 120 K) is observed for all three samples studied. We argue that the Ru-1222 system becomes (i) Anti-ferromagnetically (AFM) ordered at TM. (ii) At Tirr < TM, weak-ferromagnetism (W–FM) is induced by the canting of the Ru moments. (iii) At TC (TM/TC ~ 4), the system becomes SC and both SC and W–FM states coexist.