Magnetization study of RuSr₂Y_1.5Ce_0.5Cu₂O₁₀

We have studied the magnetic properties of nonsuperconducting RuSr₂Y_1.5Ce_0.5Cu₂O₁₀ [L=Y, Dy, and Ho (Ru-1222)] compounds synthesized under high pressure (6 Gpa) at elevated temperature. These materials become magnetically ordered at T_M=152(2) K regardless of L. The wide ferromagneticlike hysteresis loops, which open at 5 K, close themselves around T_irr=90–100 K and the remanent magnetizations (Mrem) and coercive fields (H_C) become zero. Surprisingly, at T_irr<T<TM a reappearance of the M_rem and H_C (with a peak at 120–130 K) is observed for all three samples studied. For the nonmagnetic L=Y compound, the extracted ferromagnetic moment is at 5 K and the effective paramagnetic moments are 0.75 and 2.05_μB/Ru, values which are close to the expected 1μB and 1.73μB, respectively, for the low-spin state of Ru₅₊. We argue that the Ru-1222 system becomes: (i) antiferromagnetically ordered at T_M and in this range a metamagnetic transition is induced by the external field. (ii) At T_irr<T_M, weak ferromagnetism is induced by the canting of the Ru moments.