We use Scanning Electron Microscopy with Polarization Analysis (SEMPA) to image the magnetic domain structures of individual ferromagnetic nanodisks with different diameters and thicknesses, and thereby determine the phase diagram of the magnetic ground states in these technologically important magnetic structures. Depending on the nanodisk dimensions, we observe magnetic structures based on one of three configurations: a single domain in-plane, a single domain out-of-plane, or a vortex state. By systematically imaging Ni80Fe15Mo5 nanodisks with diameters that range from 35 nm to 190 nm and with thicknesses that range from 10 nm to 65 nm, we are able to locate phase boundaries between the three different phases and the triple point. The phase boundaries are not sharply defined, however. Near the boundaries, we observe disks in a mixture of the different, metastable ground phases, and we observe variations of the basic states, such as a tilted vortex configuration. A magnetic phase diagram generated by a micromagnetic simulation is found to be in good qualitative agreement with the phase diagram determined by the SEMPA measurements. Determining the magnetic phases in the sub-100 nm nanodisks enables tailoring material properties and geometry of nanodisks for various potential applications.
Citation: Physical Review B
Pub Type: Journals
magnetic nanodisk, single domain state, magnetic vortex state, Scanning Electron Microscopy with Polarization Analysis (SEMPA), micromagnetic simulation (OOMMF)