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Parametric excitation of a magnetic nanocontact by a microwave field

We demonstrate that magnetic oscillations of a current-biased magnetic nanocontact can be parametrically excited by a microwave field applied at twice the resonant frequency of the oscillation. The threshold microwave amplitude for the onset of the oscillation decreases with increasing bias current, and vanishes at the transition to the auto-oscillation regime. The parametrically excited oscillation mode is the same as the one in the auto-oscillation regime, enabling studies of both the passive and the active dynamics of the oscillator. Theoretical analysis shows that measurements of parametric excitation provide quantitative information about the relaxation rate, the spin transfer efficiency, and the nonlinearity of the nanomagnetic system.