Flux creep measurements in the critical state for c-axis oriented YBa2Cu3O7-δ samples have been carried out in the temperature range between 0.06 and 20 K. The normalized relaxation rate of the remanent magnetization decreases with decreasing temperature below 20 K and becomes constant with the value of about 0.01 below 1 K. The relaxation rates are independent of the direction of the applied magnetic field below 4 K at least. These results are in good agreement with the prediction by quantum collective creep theory. The crossover from the quantum tunneling process to the thermal activation process of the vortex motion is observed at 3 K.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering