Vortex dynamics and magnetic anisotropy in RuSr2GdCu2O8

Polycrystalline samples of RuSr2GdCu2O8 with a magnetic ordering temperature (TM=135 K) and a resistively determined superconducting onset temperature (Tc=45 K) were synthesized using a solid-state reaction. Transport and magnetic measurements indicated coexistence of weak ferromagnetic-like order and superconductivity at low temperatures. A novel radio-frequency (rf) resonant technique was employed to probe the mixed state response. The results clearly indicate that in the superconducting state (T<Tc), the rf response is dominated by the flux lattice dynamics and in the normal state (Tc<T<TM), the data are consistent with transverse susceptibility exhibiting sharp peaks at characteristic switching and anisotropy fields.