  Spin-torque oscillators are strong candidates as nano-scale microwave
generators and detectors. However, because of large amplitude-phase coupling
(non-linearity), phase noise is enhanced over other linear auto-oscillators.
One way to reduce nonlinearity is to use ferromagnetic layers as a resonator
and excite them at localized spots, making a resonator-excitor pair. We
investigated the excitation of oscillations in dipole-coupled ferromagnetic
layers, driven by localized current at ferromagnetic nano-contacts.
Oscillations possessed properties of optical-mode spin-waves and at low field
($\approx$200 Oe) had high frequency (15 GHz), a moderate precession amplitude
(2--3$^\circ$), and a narrow spectral linewidth ($<$3 MHz) due to localized
excitation at nano-contacts. Micromagnetic simulation showed emission of
resonator's characteristic optical-mode spin-waves from disturbances generated
by domain-wall oscillations at nano-contacts.

Mesoscale and Nanoscale Physics