Fundamental magnetic states of disk and ring elements

We present here a review of our recent work on the equilibrium magnetic states in micrometer ring and disk elements (1.65 μm in diameter) with varying thickness (5–38 nm), ring width (110–730 nm) and magnetic material (fcc Co, polycrystalline hcp Co and polycrystalline fcc Ni80Fe20). The magnetic states have been studied using a variety of techniques, including magneto-optic Kerr effect magnetometry and non-invasive imaging techniques, such as photoemission electron microscopy (PEEM). In particular, we consider the effect of the magnetocrystalline anisotropy on the equilibrium magnetic states and on the magnetic switching of ring and disk elements to show that significant changes occur in the case of disk elements and wide rings. A systematic study of the remanent magnetic states in disk elements shows that several magnetic configurations are stabilised at remanence, ranging from the vortex state to other well defined multidomain states, namely a state with two vortex cores (‘diamond’ state) and a high remanence ‘triangle’ state, which are mapped according to material and thickness range. In most instances, different magnetic states coexist in an array of disks subjected to the same field history. These observations are correlated with micromagnetic simulations to show that these magnetic metastable states are stabilised by defects or attained in the nucleation process following the removal of the applied magnetic field.