Stepwise amorphization of the flux-line lattice in Ca3Rh4Sn13: A peak-effect study

The peak effect (PE) region in a single crystal of Ca3Rh4Sn13 is shown to c omprise two discontinuous first-order-like transitions located near its ons et and peak positions, in accordance with a stepwise fracturing of the flux -line lattice. Magnetization response to thermal cycling across the onset p osition produces an open hysteresis loop, consistent with the notion of the fracturing. A thermomagnetic history dependence study shows that the criti cal current density J(c)(H,T) is path dependent over a large part of the (H ,T) parameter space. Tills path dependence ceases above the peak position o f the peak effect, suggesting a complete amorphization of the flux-line lat tice at (T-p,H-p) line. A plausible vortex phase diagram has been construct ed for Ca3Rh4Sn13 in which phases like an elastic solid, a plastic solid, a nd pinned and unpinned amorphous states have been identified.