Spin glass behavior in RuSr2Gd1.5Ce0.5Cu2O10-δ

The dynamics of the magnetic properties of polycrystalline RuSr 2 Gd 1 . 5 Ce 0 . 5 Cu 2 O 1 0 - δ (Ru-1222) have been studied by ac susceptibility and dc magnetization measurements, including relaxation and ageing studies. Ru-1222 is a reported magnetosuperconductor with Ru spins magnetic ordering at temperatures near 100 K and superconductivity in Cu-O 2 planes below T c ∼40 K. The exact nature of Ru spins magnetic ordering is still being debated, and no conclusion has been reached yet. In this work, a frequency-dependent cusp was observed in Χ a c vs T measurements, which is interpreted as a spin glass transition. The change in the cusp position with frequency follows the Vogel-Fulcher law, which is commonly accepted to describe a spin-glass with magnetically interacting clusters. Such an interpretation is supported by thermoremanent magnetization (TRM) measurements at T=60 K. TRM relaxations are well described by a stretched exponential relation, and present significant aging effects.