The effects of magnetization switching on the superconducting properties of S/F bilayers and F/S/F trilayers

Abstract

We discuss different effects which are experimentally found in superconductor ( S )/ferromagnet ( F ) hybrids when the magnetization of the F -layers is inhomogeneous, or when the magnetization directions in different F -layers are not parallel. In bilayers consisting of Nb and Permalloy (Py), we find a lowering of the resistance in the superconducting transition at the coercive field <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>H</mml:mi> <mml:mi mathvariant="normal">co</mml:mi> </mml:msub> </mml:math> of the Py layer, which we attribute to the effects of domain walls. In trilayers of Cu 0.46 Ni 0.54 /Nb/Cu 0.46 Ni 0.54 we find an increase of the depairing current in the superconducting state around <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>H</mml:mi> <mml:mi mathvariant="normal">co</mml:mi> </mml:msub> </mml:math> , which is probably also due to domain walls. In trilayers of Py/Nb/Py, however, we find, besides domain wall effects from individual layers, a strong increase of the resistance in the transition when the magnetization directions of the two Py layers are switched to an antiparallel geometry. We ascribe this to the presence of spin-polarized quasiparticles.