Scan rate dependence of magnetization hysteresis in weakly pinned crystals of 2H-NbSe 2 and Ca 3 Rh 4 Sn 13 : A vibrating sample magnetometer study A.D. Thakur a,b, * , D. Pal c , M.J. Higgins d , S. Ramakrishnan a , A.K. Grover a a Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Mumbai 400 005, India b National Institute for Materials Science, 1-2-1 Sengen, Tsukuba-shi, Ibaraki 305-0047, Japan c Department of Physics, Indian Institute of Technology, Guwahati 781 039, India d Department of Physics and Astronomy, Rutgers University, Picastaway, NJ 08540, USA Received 27 February 2007; received in revised form 3 July 2007; accepted 23 July 2007 Available online 8 August 2007 Abstract We present experimental data relating to magnetic field (H) scan rate (dH/dt) dependence in the magnetization (M) hysteresis width across the field regions of the second magnetization peak (SMP) and the peak effect (PE) in weakly pinned crystals of 2H-NbSe 2 and Ca 3 Rh 4 Sn 13 . We note that the said dependence is small at the low field end, where individual/small bundle pinning dominates, as well as at the high field end (i.e., above the peak field of the PE), where disordered amorphous state is the stationary state. In between the onset field of the SMP anomaly and the peak field of PE, the scan rate dependence in magnetization data displays a non-monotonic variation. We conjecture that the healing of the transient disordered vortex states injected into a superconducting sample during field ramping process could be responsible for the observed behavior. We believe that the disordering commencing at the onset field of SMP has a window to heal between its peak field (H p smp ) and the onset field (H on p ) of the PE. A comparison of the scan rate dependence in two different crystals of 2H-NbSe 2 , one of which displays only the PE phenomenon and the other one that displays both SMP and PE anomalies, show that while enhancement in quenched random pinning invokes the occurrence of SMP anomaly, it slows down the tem- poral decay of currents across the PE region. Ó 2007 Elsevier B.V. All rights reserved. PACS: 74.60.Ge; 64.70.Dv; 74.25.Dw; 74.25.Sv Keywords: Vortex matter; Peak effect; Second magnetization peak; Order–disorder transition; Temporal decay 1. Introduction Evidences have accumulated in recent years that the peak effect (PE) phenomenon in critical current density (J c ) located at the edge of the depinning process is distinct from the second magnetization peak (SMP) anomaly com- mencing at field values deeper in the mixed state of the weakly pinned superconducting samples of several low T c and high T c compounds, e.g., Ca 3 Rh 4 Sn 13 [1], RNi 2 B 2 C (R = Y, Lu) [2],V 3 Si [3],2H-NbSe 2 [4,5], PrOs 4 Sb 12 [6], YBa 2 Cu 3 O 7 [1,7–9], etc. In collective pinning [10] scenarios, the critical current density can be related to the length scales over which the displacements of the flux lines from their equilibrium positions remain correlated. In such a framework, an anomalous increase in field/temperature (H/T) variation of J c can be construed to imply a decrease in the correlation volume over which flux lines remain elas- tically deformed and collectively pinned, thereby, leading to the notion of order–disorder transformation in the 0921-4534/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.07.009 * Corresponding author. Address: National Institute for Materials Science, 1-2-1 Sengen, Tsukuba-shi, Ibaraki 305-0047, Japan. E-mail addresses: thakur.ajay@nims.go.jp (A.D. Thakur), grover@ tifr.res.in (A.K. Grover). www.elsevier.com/locate/physc Physica C 466 (2007) 181–189