Josephson junction through a thin ferromagnetic layer: negative coupling

Phys Rev Lett. 2002 Sep 23;89(13):137007. doi: 10.1103/PhysRevLett.89.137007. Epub 2002 Sep 9.


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 ("pi") coupling, in agreement with theoretical calculations.