Agility of vortex-based nanocontact spin torque oscillators

We study the agility of current-tunable oscillators based on a magnetic vortex orbiting around a point contact in spin valves. The theory predicts that frequency tuning by currents occurs at constant orbital radius so an exceptional agility is anticipated. To test this, we have inserted an oscillator in a microwave interferometer to apply abrupt current variations while time resolving its emission. Using frequency shift keying, we show that the oscillator can switch between two stabilized frequencies differing by 25% in less than ten periods. With a wide frequency tunability and a good agility, such oscillators possess desirable figures of merit for modulation-based rf applications.