PEAK-EFFECT IN HTSC CERAMICS AT A LOW MAGNETIC-FIELD

It was investigated the dependence of critical current Jc in ceramic samples on a magnetic field H. Peak-effect was observed in ceramics with large size of the grains. The curve JC(H) has a minimum near the first critical magnetic field of grains. The effect decreases and position of minimum displaces to high magnetic field with decreasing of the temperature. Experimental dependence of JC(H) has no peak-effect in the samples with small size of grains. To explain experimental results we employ a model of HTSC ceramics, which consists of grains, coupled by weak links. When the Abricosov vortices are in the grains with concentration n, the critical current of these links in magnetic field is higher, than without vortices. The effect is displayed distinctly at the condition nλL ≫1 where λ - London penetration depth, L - a size of grains. As a result, the dependence JC(H) for the whole sample occurs non-monotonic. © 1990.