Observation of a Transition From Inverse-Spin-Switch to Spin-Switch Behavior in Domain State of a Py/Nb/Py Trilayer

We study spin switch behavior of the six bridges of bare, or pseudo spin-valve Py/Nb/Py trilayer prepared on a single chip. Magnetization measurement of both longitudinal and transverse moment on a large companion sample reveals that a significant amount of transverse component exists in the antiparallel domain (AD) state, which is originated in stray magnetic field from domain walls. The stray magnetic field induces flux lines into the Nb layer and the motion of these flux lines under the force exerted by the bias current is the main origin for inverse spin switch effect observed in the AD state of most bridges. In addition to inverse spin switch effect, we observe a peculiar behavior of a transition from inverse spin switch to spin switch behavior with decreasing temperature in one of six bridges. In order to understand the extraordinary behavior, we first note that the flux pinning should be present in this particular sample to suppress the dissipation by flux motion, then we propose that when the domain structure incidentally matches underlying distribution of pinning sites, spin switch effect in the AD state can occur by domain wall superconductivity and/or proximity effect.