Nonequilibrium order-disorder vortex transitions in (formula presented)

Magneto-optical snapshots of the induction distribution across a (formula presented) crystal subjected to ramped magnetic fields reveal strong effects of transient disordered vortex states near the disorder-driven vortex phase transition. These transient states, predominantly generated by edge contamination during field ascending and by supercooling of the disordered vortex lattice during field descending, cause smearing of the transition and shift of its onset towards lower inductions. With decreasing temperature, these effects are more pronounced as the lifetime of the transient vortex states increases. Similar effects are observed with increasing field sweep rates, as transient states with shorter lifetime play a role. These observations clarify previously reported puzzles, e.g., the absence of the second magnetization peak at low temperatures, its appearance at longer times, and the shift of its onset to lower inductions for higher field sweeping rates.