Dynamic exchange coupling in magnetic bilayers
  A long-ranged dynamic interaction between ferromagnetic films separated by normal-metal spacers is reported, which is communicated by nonequilibrium spin currents. It is measured by ferromagnetic resonance (FMR) and explained by an adiabatic spin-pump theory. In FMR the spin-pump mechanism of spatially separated magnetic moments leads to an appreciable increase in the FMR line width when the resonance fields are well apart, and results in a dramatic line-width narrowing when the FMR fields approach each other. 
Bret Heinrich, Yaroslav Tserkovnyak, Georg Woltersdorf, Arne Brataas,   Radovan Urban, and Gerrit E. W. Bauer