We study vortex pattern formation in thin ferromagnetic films under the action of strong spin-polarized currents. Considering the currents which are polarized along the normal of the film plane, we determine the critical current above which the film goes to a saturated state with all magnetic moments being perpendicular to the film plane. We show that stable square vortex-antivortex superlattices (vortex crystals) appear slightly below the critical current. The melting of the vortex crystal occurs with further decrease of current. A mechanism of current-induced periodic vortex-antivortex lattice formation is proposed. Micromagnetic simulations confirm our
analytical results with a high accuracy.
Phys. Rev. B. 92, 144401 (2012), PDF.