Controllable vortex polarity switching by spin polarized current

Nanopillars containing a perpendicular polarizer and a vortex free layer have been considered as promising structures for the selective switching of the vortex core by changing the spin polarized current direction. In this paper, two distinct switching routes of the vortex cores are found to be classified according to the lateral dimension of samples. For a relatively large element, the core polarity is switched through a creation and annihilation process of vortex-antivortex pair and the vortex circulation remains unchanged; however, for a small element, the core switching is mediated by a transient C-state, and moreover, the circulation is dominated by the current-generated Oersted field.