Determination of U(x,t) and j in MTG YBCO bulk by magneto-optic imaging

We use the magneto-optic imaging to determine the spatial distribution and the time dependence of the magnetic induction B-z(x,t) on the broad surface of the melt texture growth YBCO bulk. The model-independent effective acti vation energy U and the current density j could be calculated from B-z(x,t) , partial derivativeB(z)(x,t)/partial derivativet and partial derivativeB(z )(x,t)/partial derivativex. The good fit shows that the thermally activated flux creep in the melt texture growth bulk is consistent with the logarith mic model in the temperature range of liquid nitrogen.