Scan rate dependence of magnetization hysteresis in weakly pinned crystals of 2H-NbSe2 and Ca3Rh4Sn13: A vibrating sample magnetometer study

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-NbSe2 and Ca3Rh4Sn13. 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 (Hsmpp) and the onset field (Hpon) of the PE. A comparison of the scan rate dependence in two different crystals of 2H-NbSe2, 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 temporal decay of currents across the PE region.