Streubel, R.; Kronast, F.; Reiche, C.F.; Muehl, T.; Wolter, A.U.B.; Schmidt, O.G.; Makarov, D.: Vortex circulation and polarity patterns in closely packed cap arrays. Applied Physics Letters 108 (2016), p. 042407/1-4
We studied curvature-driven modifications to the magnetostatic coupling of vortex circulation and polarity in soft-magnetic closely packed cap arrays. A phase diagram for the magnetic remanent/ transition states at room temperature as a function of diameter and thickness was assembled. For specimens with vortex remanent state (40 nm-thick Permalloy on 330 nm spherical nanoparticles), both vortex circulation and polarity were visualized. Intercap coupling upon vortex nucleation leads to the formation of vortex circulation patterns in closely packed arrays. The remanent circulation pattern can be tailored choosing the direction of the applied magnetic field with respect to the symmetry axis of the hexagonal array. An even and random distribution of vortex polarity indicates the absence of any circulation-polarity coupling.