  Magnetization dynamic response of coupled and uncoupled spin valves with
structure NiFe(20 nm)/Cu(t_Cu)/NiFe(20 nm)/IrMn(10nm) were probed using
broadband ferromagnetic resonance absorption measurements. By varying the Cu
thickness t_Cu we were able to tailor the coupling intensity between the free
and pinned layers. Broadband spectra show two resonant modes for each measured
field. It is noticed that the coupling among NiFe layers modifies the amplitude
of the absorption peaks and, moreover, the dispersion relations of the modes,
which are distorted specially at the anti-parallel state. A numerical model is
proposed and applied to address the underlying physics and the observed
properties of these systems.
