Magnetic force microscope tip-induced remagnetization of CoPt nanodisks with perpendicular anisotropy

We report on the results of a magnetic force microscopy investigation of remagnetization processes in arrays of CoPt nanodisks with diameters of 35 and 200 nm and a thickness of 9.8 nm fabricated by e-beam lithography and ion etching. The controllable magnetization reversal of individual CoPt nanodisks by the magnetic force microscope (MFM) tip-induced magnetic field was demonstrated. We observed experimentally two essentially different processes of tip-induced remagnetization. Magnetization reversal of 200 nm disks was observed when the probe moved across the particle while in case of 35 nm nanodisks one-touch remagnetization was realized. Micromagnetic modeling based on the Landau-Lifshitz-Gilbert (LLG) equation demonstrated that the tip-induced magnetization reversal occurs through the essentially inhomogeneous states. Computer simulations confirmed that in case of 200 nm disks the mechanism of embryo nucleation with reversed magnetization and further dynamic propagation following the probe moving across the particle was realized. On the other hand one-touch remagnetization of 35 nm disks occurs through the inhomogeneous vortexlike state. Micromagnetic LLG simulations showed that magnetization reversal in an inhomogeneous MFM probe field has a lower energy barrier in comparison with the mechanism of coherent rotation, which takes place in a homogeneous external magnetic field