Effect of parallel and antiparallel configuration on magnetic damping in Co/Ag/Co/Gd

When two ferromagnetic layers have a common resonance frequency, the usual spin-pumping broadening may be reduced by dynamic exchange coupling. Utilizing the antiferromagnetic coupling between Co and Gd, we explore the change in ferromagnetic resonance accompanying a spontaneous transition from parallel to antiparallel magnetic alignment of two Co films below the compensation temperature T-comp. Above T-comp, the data are consistent with conventional models. However, a rapid doubling of magnetic damping accompanies the realignment, which is reminiscent of resistivity changes in giant magnetoresistance. (C) 2011 American Institute of Physics. [doi:10.1063/1.3592298]