Spin torque effect on topological defects and transitions of magnetic domain phases in Ta/CoFeB/MgO

Using the polar magneto-optical Kerr effect microscope, we have observed in a prototypical multilayer system of Ta/CoFeB/MgO a spin current-driven transformation of an initial labyrinthine domain pattern. The labyrinthine domain phase can either transform into a dense array of skyrmions or simply change in the orientational order, depending on the strengths of the applied spin current pulse and the external magnetic field. We conclude both from experimental studies and from micromagnetic simulations that the applied spin current leads to the generation/deletion of topological defects through modifying the motion of domain walls and the magnetic configurations within the domain walls, leading to the observed transformations. This is different from the thermally induced transitions where the nucleation and proliferation of topological defects are the dominant factors.