Confinement of Magnetic Vortex and Domain Walls in Dipolar-Coupled Concentric Nanocylinders

We report a theoretical study of the magnetic phases of core-shell nanocylinders, consisting of a Py cylindrical core, dipolar coupled to a coaxial Fe cylindrical shell. A few nanometers thick nonmagnetic cylindrical layer separates the core from the shell, and controls the magnitude of the core-shell dipolar interaction. New magnetic phases emerge from the dipolar interaction, and may consist of either the combination of the intrinsic magnetic phases or new phases that are not seen in isolated cylinders and shells. We discuss typical examples. The magnetic phases of a 21 nm-height nanocylinder composed of a 57 nm-diameter Py core coupled to a 12 nm-thick Fe shell may be set to be a Py vortex with the same chirality of the Fe shell circular state, or a Py uniform domain coupled to a pair of domain walls of the Fe shell onion state. A magnetic vortex may be stabilized in a 6 nm-height, 42 nm-diameter Py cylinder coupled to a 6 nm-thick Fe shell.