Nonlinear frequency and amplitude modulation of a nanocontact-based spin-torque oscillator

We study the current-controlled modulation of a nanocontact spin-torque oscillator. Three principally dif-ferent cases of frequency nonlinearity (d2f/dIdc2 being zero, positive, and negative) are investigated. Standardnonlinear frequency-modulation theory is able to accurately describe the frequency shifts during modulation. However, the power of the modulated sidebands only agrees with calculations based on a recent theory of combined nonlinear frequency and amplitude modulation.