Low field magnetic relaxation of superconducting C₆₀Rb₃

The relaxation of magnetization M in superconducting C₆₀Rb₃ have been measured at different temperature ranges in low magnetic fields below T_c to explore the flux pinning. The measurements were performed with a superconducting quantum interference magnetometer. The applied magnetic field was 300 G - 600 G and the measured time at each temperature was 1 × 10⁴ sec. M versus 1nt shows a linear behavior for t ≥ 3600 sec. The data were analyzed in the framework of the flux pinning model of Anderson-Kim. The analyses give the activation energy of U(5K) ≈ 20 mev, and the critical current density based on J_c(T) ∝ [dM/dlnt] × [U/kT] shows J_c ∝ (1-t)^m, with the exponent m ≈ 2.0. The results are discussed.