Anomalous magnetic behavior in YSr₂(Ru_0.8Cu_0.2)O₆

Magnetic studies on ceramic YSr₂(Ru_0.8Cu_0.2)O₆ annealed at 1200°C and further annealed at 1350°C are presented. None of the samples studied is superconducting. Annealing at 1350°C leads to a Type 1 antiferromagnetic (AFM) structure (T_N∼30K), and suggests a similarity to all other RSr₂RuO₆ (R=Y, Eu,Gd and Er) compounds. On the other hand, the 1200° C annealed material exhibits an additional independent magnetic structure with T_M∼130K, which is magnetically coupled with the AFM structure. Irreversibility in the zero-field-cooled field-cooled curves appears only at low applied magnetic fields (H<2.5kOe). The positive remanent becomes negative above T_N and vanishes at T_M. The second magnetic structure shows the characteristics of short-range magnetic interactions, possibly as spin glass like behavior. The stark contrast between the samples is surprising, because the two compounds are chemically and structurally identical.