Three-mode behavior of spin-transfer vortex oscillators with dynamic polarizer

Magnetic vortex-based oscillators represent a unique opportunity to study the mutual spin-transfer torque coupling between two ferromagnetic layers in a spin-valve configuration. This will eventually lead to a complete understanding of this phenomenon and, potentially, to electronic devices of practical application. Mutual spin-transfer torque can lead to multiple-mode high-frequency dynamics in a spin-valve system. We here report our study on the emission response of an ohmic nanocontact to a spin-valve multilayer subject to perpendicularly applied magnetic field. In this configuration, three modes are accessible, two of which correspond to the precessional motion of a vortex in one of the two ferromagnetic layers with the other working as a static polarizer. At high currents, the third mode can be observed that is ascribed to the simultaneous precession of two vortices, one in each layer, with the other layer working as a dynamic polarizer. The simultaneous application of a field in the sample plane tends to suppress the mode that corresponds to the precessional motion of the vortex in the thinner ferromagnetic layer.