Magnetic vortices in Sub-100 nm magnets

Presented is a quantitative study of the magnetic vortex state and the vortex core in sub-100 nm magnetic dots. Arrays of magnetic nanodots covering over 1 cm
²
are fabricated using self-assembled nanopores in anodized alumina. Transition from a vortex to a single domain state for the Fe dots is studied by magnetization measurements (SQUID, VSM, and MOKE) as a function of the dots size and magnetic field. Micromagnetic and Monte Carlo simulations confirm the experimental observations. Thermal activation and exchange bias have a large effect on the vortex nucleation field. Quantitative analysis of grazing incidence small angle neutron scattering measurements with polarization analysis, performed on 65 nm Fe dots yields the magnetization of the vortex core of 140±50 emu/cm
³
and its diameter of 19±4 nm, in agreement with the simulations results.