We have employed complete micromagnetic simulations to analyze dc current driven self-oscillations of a vortex core in a spin-valve nanopillar in a perpendicular field by including the coupled effect of the spin-torque and the magnetostatic field computed self-consistently for the entire spin-valve. The vortex in the thicker nanomagnet moves along a quasielliptical trajectory that expands with applied current, resulting in "blueshifting" of the frequency, while the magnetization of the thinner nanomagnet is nonuniform due to the bias current. The simulations explain the experimental magnetoresistance-field hysteresis loop and yield good agreement with the measured frequency versus current behavior of this spin-torque vortex oscillator.
Bibliographical noteFunding Information:
This work was partially supported by Spanish Projects under Contract Nos. SA025A08 and MAT2008-04706/NAN. This research was also supported in part by the Office of Naval Research/MURI program and by the National Science Foundation through the NSEC program support for the Center for Nanoscale Systems (contract No. EEC-0646547). Additional support was provided by NSF through use of the facilities of the Cornell Nanoscale Facility-NNIN and the facilities of the Cornell Center for Materials Research, an NSF MRSEC.
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