Field-history-dependent peak effect in the superconducting mixed state of CeRu2

Detailed magnetization measurements of CeRu2 single crystals with different purity are performed in order to clarify whether their peak effects are du e to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) transition. The onset fiel d of the peak shifts to lower held side as the sample becomes impure. Regar dless of the purity the Ginzburg-Landau parameter kappa(2) continues to inc rease on cooling from T-c, indicating little paramagnetic suppression of th e superconductivity. These results disagree with the scenario of the FFLO t ransition. (C) 1999 Elsevier Science B.V, All rights reserved.