Magnetic k π -skyrmions and their field-driven evolutions in a nanostructured centrosymmetric magnet

Magnetic k π -skyrmions are rotationally symmetric vortex-like solitons, whose magnetization rotates by an angle of k π from its center to outermost boundary. Here, we report k π -skyrmions ( k = 2, 3, and 4) and their field-driven magnetic evolutions in centrosymmetric uniaxial ferromagnetic Fe ₃Sn ₂ nanodisks. We show that zero-field non-axisymmetric k π -skyrmions turn to be axisymmetric after applying an out-of-plane field. The collapses of ( k + 1 ) π -skyrmions to k π -skyrmions induced by external field are also experimentally identified. Furthermore, numerical simulations well reproduce experimental magnetization mapping of k π -skyrmions and further demonstrate their three-dimensional magnetic structures.