Micromagnetic analysis of nonlinear dynamics in spintronic analog modulators

The simultaneous action of dc and ac spin-polarized current traversing a magnetic nanocontact device results in a combined amplitude-frequency nonlinear modulation process, a promising application of spin-transfer oscillators. A micromagnetic analysis of the nonlinear magnetization dynamics occurring in such devices is carried out in both spatial and frequency domain. Numerical results show that the proposed combined modulation scheme affects the amplitude of the sidebands as well as their phase, and remark a substantial difference with respect to the properties exhibited by a classical linear modulator. Further investigations performed as function of the frequency of the modulating signal allow to establish that, when the modulating frequency approaches the carrier one, no modulation occurs and a frequency pulling, typical of injection locking phenomena, takes place instead.