Observation of power-law time relaxation of the magnetization of a LuBa2Cu3O7 single crystal

A power-law dependence of the time relaxation of the magnetization in a LuBa2Cu3O7 single crystal has been observed over wide temperature and magnetic-field ranges. For T<30 K, the decay rate S=lnM(t)/lnt is a linear function of T and can be expressed as S=β(T)+δ, where δ is a constant decreasing with the increase of the applied field. By fitting β(T) with a recent theoretical model, it is found that the effective pinning energy Ue is independent of T and decreases logarithmically with the increase of the applied field. By comparing the values of δ with β(T), it is concluded that at the low-temperature region, the magnetization relaxation is dominated by an unknown temperature-independent ''tunneling'' effect. The total relaxation rate can be expressed as S=[kBT/(1.18-0.24 log10H)]+63.11H-0.84