  Excitation of magnons or spin-waves driven by nominally unpolarized transport
currents in point contacts of normal and ferromagnetic metals is probed by
irradiating the contacts with microwaves. Two characteristic dynamic effects
are observed: a rectification of off-resonance microwave current by spin-wave
nonlinearities in the point contact conductance, and a resonant stimulation of
spin-wave modes in the nano-contact core by the microwave field. These
observations provide a direct evidence that the magnetoconductance effects
observed are due to GHz spin dynamics at the ferromagnetic interface driven by
the spin transfer torque effect of the transport current.
