Magnetic coupling in mesoscopic metal/ferromagnet layered systems
  We consider a mesoscopic mechanism of the exchange interaction in a system of alternating ferromagnetic/nonmagnetic metallic layers. In the case of small mesoscopic samples the sign and the amplitude of the exchange energy turn out to be random sample specific quantities. They can be changed by applying an external magnetic field, by attaching to the system superconducting electrodes with different phases of the superconducting order parameter and by changing the chemical potential of electrons in the matal with the help of a gate. In the case of square or cubic geometries of the nonmagnetic layer at low temperature the variance of the exchange energy turns out to be sample size independent. 
B.Spivak, A.Zyuzin