  Current-induced excitations in bilayer magnetic nanopillars have been studied
with large magnetic fields applied perpendicular to the layers at low
temperature. Junctions investigated all have Cu/Co/Cu/Co/Cu as core layer
stacks. Two types of such junctions are compared, one with the core stack
sandwiched between Pt layers (type A), the other with Pt only on one side of
the stack (type B). Transport measurements show that these two types of
junctions have similar magnetoresistance and slope of critical current with
respect to field, while A samples have higher resistance. The high-field
bipolar excitation, as was previously reported [Oezyilmaz et al., Phys. Rev. B
71, 140403(R) (2005)], is present in B samples only. This illustrates the
importance of contact layers to spin-current-induced phenomena. This also
confirms a recent prediction on such spin-wave excitations in bilayers.
