The second magnetization peak and the peak effect phenomenon in the superconductor Ca3Rh4Sn13

We report on the observation of the anomalous second magnetization peak (SM P) and the peak effect (PE) in juxtaposition to each other in the isotherma l magnetization hysteresis loops at T less than or equal to 4 K in a weakly pinned single crystal of an isotropic superconductor Ca3Rh4Sn13 (T-c appro ximate to 8.2 K). The position of the SMP does not display any temperature variation, whereas the PE appearing at the edge of the irreversibility line progressively moves towards lower fields as temperature increases. At T ap proximate to 5 K, the PE nearly swamps the SMP, and above this temperature only the PE can be observed. if the SMP and the PE can be construed as repr esenting changes in the spatial order of the flux line lattice (FLL), the a pparent merger of loci of the peak fields of the SMP and the PE in the neig hborhood of H approximate to 15 kOe at a reduced temperature a [= T/T-e(0)] of about 0.6 could imply the existence of a multi-critical point. (C) 2001 Elsevier Science B.V, All rights reserved.