Inverse proximity effect in superconductor-ferromagnet bilayer structures.

Measurements of the polar Kerr effect using a zero-area-loop Sagnac magnetometer on Pb/Ni and Al/(Co-Pd) proximity-effect bilayers show unambiguous evidence for the "inverse proximity effect," in which the ferromagnet induces a finite magnetization in the superconducting layer. To avoid probing the magnetic effects in the ferromagnet, the superconducting layer was prepared much thicker than the light's optical-penetration depth. The sign and size of the effect, as well as its temperature dependence agree with recent predictions by Bergeret et al. [Phys. Rev. B 69, 174504 (2004)]10.1103/PhysRevB.69.174504.