Vortex dynamics and magnetic anisotropy in RuSr2GdCu2O8

Polycrystalline samples of RuSr2GdCu2O8 with a magnetic ordering temperature (T-M = 135 K) and a resistively determined superconducting onset temperature (T-c = 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 < T-c), the rf response is dominated by the flux lattice dynamics and in the normal state (T-c < T < T-M), the data are consistent with transverse susceptibility exhibiting sharp peaks at characteristic switching and anisotropy fields. (C) 2001 American Institute of Physics.