We investigate Josephson coupling through a ferromagnetic thin film using Superconductor-Insulator-Ferromagnet-Superconductor planar junctions. Damped oscillations of the critical current are observed as a function of the ferromagnetic layer thickness. We show that they result from the exchange energy gained or lost by a quasiparticle Andreev-reflected at the ferromagnet-superconductor interface. The critical current cancels out at the transition from positive ("0") to negative ("π") coupling, in agreement with theoretical calculations.
@article{arxiv.cond-mat/0201104,
title = {Feromagnetic "$\pi$"-junctions},
author = {T. Kontos and M. Aprili and J. Lesueur and F. Genet and B. Stephanidis and R. Boursier},
journal= {arXiv preprint arXiv:cond-mat/0201104},
year = {2007}
}