Impurity-assisted interlayer exchange coupling across a tunnel barrier.

Localized impurity or defect states in the insulating barrier layer separating two ferromagnetic films affect dramatically the interlayer exchange coupling (IEC), making it significantly stronger compared to perfect barriers. We demonstrate that the impurity-assisted IEC becomes antiferromagnetic if the energy of the impurity states matches the Fermi energy and that the coupling strength decreases with temperature. These results explain available experimental data on the IEC across tunnel barriers.