Spin-flip scattering and non-ideal interfaces in dirty ferromagnet/superconductor junctions

Abstract

We study the proximity-induced superconducting correlations as well as the local density of states of a ferromagnet, in a ferromagnet/s-wave superconductor heterostructure. We include the effects of spin-flip scattering, non-ideal interfaces, and the presence of impurities in the sample. We employ the quasiclassical theory of superconductivity, solving the Usadel equation with emphasis on obtaining transparent analytical results. As our main result, we report that in a certain parameter regime the spatial oscillations of the anomalous (superconducting) part of the Green's function induced in the ferromagnet by the proximity effect from the s-wave superconductor, are damped out due to the presence of spin-flip processes. As a consequence, spin-flip scattering may under certain conditions actually enhance the local density of states due to the oscillatory behaviour of the latter in ferromagnet/superconductor structures. We also conjecture that the damping could be manifested in the behaviour of the critical temperature ($T_c$) of the s-wave superconductor in contact with the ferromagnet. More specifically, we argue that the non-monotonic decrease of $T_c$ in ferromagnet/s-wave superconductor junctions without magnetic impurities is altered to a monotonic, non-oscillatory decrease when the condition $1>16\tau_\text{sf}^2h^2$ is fulfilled, where $\tau_\text{sf}$ is the spin-flip relaxation time and $h$ is the exchange field.