Resistance of ceramic samples: 2D localization and time dependence

In this paper, we report results of giant magnetoresistance obtained in a ceramic sample. The results show that between 40 mK and 30 K, the resistance increases as log(T) when temperature decreasing, which could be associated with the two-dimensional weak localization effect. The time dependence of the resistance after changing the magnetic field was also measured at different temperatures. At temperatures higher than 2 K, the decay of resistance is associated with the decay of the magnetization. Bellow this temperature, however, the observed large variation of the resistance with time after changing the magnetic field may be associated with the reconfiguration of magnetic structure.