  Ferromagnetic resonance (FMR) in magnetic multilayers of type F1/f/F2, where
two strongly ferromagnetic layers F1 and F2 are separated by a weakly magnetic
spacer f with a compositional gradient along its thickness, is investigated.
The method allows to detect the weak signal from the spacer in additional to
the more pronounced and readily measured signal from the outer
strongly-magnetic layers, and thereby study the properties of the spacer as
well as the interlayer exchange interaction it mediates. Variable temperature
FMR measurements, especially near the relevant Curie points, reveal a rich set
of properties of the exchange interactions in the system. The obtained results
are useful for designing and optimizing nanostructures with
thermally-controlled magnetic properties.
