Peak effect in CeRu2:: Role of crystalline defects

We measured the electrical resistivity in magnetic fields and the Hall voltage to understand the peak effect in a superconductor with the cubic structure CeRu2. Two samples with residual resistivity ratios of rho(RT)/rho(0) = 240 and 12 were prepared, and the experimental results in the superconducting mixed state were compared between them. The flux flow begins at a high field and the peak effect is observed in a very narrow window in the T vs. H phase diagram near the upper critical field H-c2 for the sample with rho(RT)/rho(0) = 240, while it starts at a lower field and the window where the peak effect is observed becomes wider for the sample with rho(RT)/rho(0) = 12. These characteristic features are mainly related to crystalline defects in the sample.