Pair breaking effects on upper critical fields in ferromagnet/superconductor layered structures

The influence of magnetic and spin–orbit impurity scattering on the upper critical fields Hc2 in ferromagnet/superconductor (F/S) hybrid structures is theoretically investigated. The generalized Usadel equations which are a pair of coupled equations containing additional spin–orbit and magnetic impurity scattering are shown to be decoupled in spite of the coupling interaction between the spin exchange field and the spin–orbit interaction in the F layer. The temperature dependence of the parallel upper critical field in the F/S bilayer is shown to be less prominent in the presence of the spin–orbit and the spin–flip scattering processes. The interplay between the zero- and pi-phases is analyzed in the case of the F/S multilayers. The pi-phase formation is found to be feasible through the strong oscillation of the zero temperature upper critical fields versus the thickness of the ferromagnetic layer. Our results which are valid in wide range of parameters may be very important for comparison with experimental data.