Vortex ferromagnetic domain structures of ferromagnetic CoFe2O4 nanodisks formed by local crystallization using a heated atomic force microscope tip

Magnetic domain structures of CoFe2O4 nanodisks were investigated by magnetic force microscopy (MFM). A CoFe2O4 thin film was deposited on a Pt/TiO2/SiO2/Si substrate using a spin coating process. Locally crystallized CoFe2O4 nanodisks were formed by local annealing with a heated atomic force microscopy tip at a fixed temperature of 700 °C. By controlling the local heating time, the diameters of the CoFe2O4 nanodisks with ferromagnetic domains were systematically adjusted over the range from 150 to 300 nm. MFM observations showed that the 150 nm CoFe2O4 nanodisks had magnetic domains with a vortex shape along the in-plane direction, with the magnetic spin oriented along the out-of-plane direction at the center of the nanodisk.