Observation of hybrid magnetic skyrmion bubbles in Fe₃Sn₂ nanodisks

It is well known that there are two types of magnetic bubbles in uniaxial magnets. Here, using Lorentztransmission electronic microscopy magnetic imaging, we report the direct experimental observation of three-dimensional (3D) type-III hybrid bubbles, which comprise Neel-twisted skyrmion bubbles with topological charge Q = -1 in near-surface layers and type-II bubbles with Q = 0 in interior layers, in Fe3Sn2 nanodisks. Using the tilted magnetic field, we further show the controlled topological magnetic transformations of three types of bubbles in a confined ferromagnetic nanodisk. Our observations are well reproduced using micromagnetic simulations based on measured magnetic parameters. Our results advance fundamental classification and understanding of magnetic bubbles, which could propel the applications of 3D magnetism.