Manifestation of modulation in spatial order of flux line lattice in weakly pinned superconductors : a vibrating sample magnetometer study

Abstract

We have investigated the healing of transient disordered vortex states injected into a superconducting sample during the field ramping process in isothermal M-H measurements as a prescription to comprehend the modulation in the state of order of the underlying equilibrium vortex state in weakly pinned single crystals of $2H$-NbSe$_2$ (zero field transition temperature, $T_c(0) \sim 6 K$) and Ca$_3$Rh$_4$Sn$_{13}$ ($T_c(0) \sim 8.2 K$), which display order-disorder transition(s). Our results reaffirm the notion that spatial order in the flux line lattice proceeds to the amorphous state in two distinct steps as evidenced by the presence of second magnetization peak (SMP) anomaly and the peak effect (PE) phenomenon. Disordering commencing at the onset field of SMP has a window to heal between its peak field ($H_{smp}^p$) and the onset field ($H_p^{on}$) of the PE. A comparison of the scan rate dependence of magnetization hysteresis widths 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 enhancment in quenched random pinning invokes the occurence of SMP anomaly, it slows down the temporal decay of currents across the PE region.