  We have measured spin-transfer-driven, large amplitude, current hysteretic,
low frequency (< 500 MHz), narrowband oscillations in nanocontacts made to spin
valve structures. The oscillations occur in zero field, persist up to 5 mT for
in plane applied fields, and to beyond 400 mT for out of plane fields. Unlike
previous measurements, the oscillation frequency is well below that for
uniform-mode ferromagnetic resonance, is only a weak function of applied field,
and is highly anharmonic. The oscillations are hysteretic with applied dc
current, appearing at high currents but persisting to lower currents upon
decrease of the current. We suggest that these observations are consistent with
the dynamics of a nonuniform magnetic state in the vicinity of the contact
nucleated by both the spin transfer torque and dc current-generated Oersted
fields, with the dynamics driven by spin transfer. The electrical oscillation
amplitudes are large and narrowband, with the largest amplitudes on the order
of 1 mV and the narrowest linewidths below 1 MHz.
