Magnetization evolution in a Permalloy dot driven by spin-polarized currents in multi-nanocontact geometry

Magnetization evolution in a Permalloy dot with radius R=200 nm and thickness L=10 nm driven by spin polarized currents was studied by micromagnetic simulations with three point contacts on a diameter. We obtained rich phase diagrams through changing the directions, magnitudes and the inter-distances of the spin-polarized currents. The current must exceed a minimum value before changes in the magnetic state occurred. As the current density was increased, the ground state changed from a single vortex state to complex magnetic states via nucleation and annihilation of vortex-antivortex pairs. However, these rich magnetization phases finally recovered into two different stable vortex states after the current was powered off.