Magnetic hedgehog-like nanostructures

Granular $CoCrPt–SiO2$ films with perpendicular magnetic anisotropy were deposited onto arrays of $SiO2$ nanoparticles with diameters down to 10 nm. Columnar CoCrPt grains with their $c$-axis pointing perpendicular to the particle surface were formed, creating a unique hedgehog-like cap structure. This peculiar structure induced by the curvature of the particles substantially modifies the magnetic properties. Underneath the CoCrPt pillars a continuous Co-rich layer was observed, which gives rise to enhanced intergranular exchange coupling resulting in single domain states. The temperature dependence of the coercivity and the angular dependence of the switching field were extracted and correlated with the microstructure.