Vortex-dynamics-mediated low-field magnetization switching in an exchange-coupled system

An aspect of a magnetic vortex whose dynamics strongly affects the magnetic structures of the environment is experimentally shown. We exploit a nanodot of an exchange-coupled bilayer with a soft magnetic Ni₈₁Fe₁₉ [permalloy (Py)] having a magnetic vortex and a perpendicularly magnetized L1₀-FePt exhibiting a large switching field (Hsw). The vortex dynamics with azimuthal spin waves makes the excess energy accumulate in the Py, which triggers reversed-domain nucleation in L1₀-FePt at a low magnetic field. Our experimental and numerical results shed light on the essence of reversed-domain nucleation, and provide a route for efficient Hsw reduction.