  We consider theoretically the impact of Rashba spin-orbit coupling on spin
torque oscillators (STOs) in synthetic ferromagnets and antiferromagnets that
have either a bulk multilayer or a thin film structure. The synthetic magnets
consist of a fixed polarizing layer and two free magnetic layers that interact
through the Ruderman-Kittel-Kasuya-Yosida interaction. We determine
analytically which collinear states along the easy axis that are stable, and
establish numerically the phase diagram for when the system is in the STO mode
and when collinear configurations are stable, respectively. It is found that
the Rashba spin-orbit coupling can induce anti-damping in the vicinity of the
collinear states, which assists the spin transfer torque in generating
self-sustained oscillations, and that it can substantially increase the STO
part of the phase diagram. Moreover, we find that the STO phase can extend deep
into the antiferromagnetic regime in the presence of spin-orbit torques.
