Clean-limit pair breaking and two-dimensional vortex dynamics in ferromagnet-superconductor heterostructures

Abstract

Superconductivity in YBa₂Cu₃O₇ films of thickness d_Y lt;500 λ sandwiched between ferromagnetic and nonmagnetic epitaxial layers has been probed. The irreversibility temperatureT_irr(H) in the vortex state maps onto a clean-limit pair-breaking temperature T_c(H), and a universal relation exists between the pair-breaking field H_pb and an effective thickness d_eff(lt;d_Y) of the superconductor. The vortex response in these two-dimensional (2D) films indicates a crossover temperature T*, which separates two regimes of flux motion controlled by formation of dislocations (Tgt;T*), and migration of preexisting dislocations and dislocation pairs (Tlt;T*) in the 2D flux line lattice.