Temperature Dependence of Glassy Exponent in YBa2Cu3O7-δ Films

Precise measurements of magnetic moment relaxation of YBa2Cu3O7-δ films were carried out in temperature range 4.2 K < T < 80 K at low magnetic field H ≈ 910 Oe. Temperature dependence of the glassy exponent μ of dependence of the activation energy U for vortices motion on current J was analyzed. It was obtained that μ increases from negative values at low temperatures T ≤ 10 K to μ ≈ 1–2 at T ≈ 40 K and decreases down to negative values at high temperatures T ≥ 70 K. It was shown that widely used Maley's technique and analysis of T/S(T) vs 1/J(T) dependence are unable to describe correctly strong μ(T) dependence observed in our experiments.