  Spin-torque driven ferromagnetic resonance (ST-FMR) is used to study magnetic
excitations in Co/Ni synthetic layers confined in nanojunctions. Field swept
ST-FMR measurements were conducted with a magnetic field applied perpendicular
to the layer surface. The resonance lines were measured under low amplitude
excitation in a linear response regime. The resulting resonance fields were
compared with those obtained using conventional rf field driven FMR on extended
films with the same Co/Ni layer structure. A lower resonance field is found in
confined structures. The effect of both dipolar fields acting on the Co/Ni
layer emanating from other magnetic layers in the device and finite size
effects on the spin wave spectrum are discussed.
