Anomalous magnetic behavior in YSr2(Ru0.8Cu0.2)O6

Magnetic studies on ceramic YSr2(Ru0.8Cu0.2)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 (TN∼30 K), 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 TM∼130 K, 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<2.5 kOe). The positive remanent becomes negative above TN and vanishes at TM. 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.