Nonuniform micromagnetic states in thin permalloy disk

As the diameter of the permalloy thin film becomes larger than some critical size, the quasiuniform state turns out to be unstable and transforms to a new nonuniform state. As the particleʹs diameter increases, the magnetization curvature increases gradually so that the average magnetization of this new nonuniform state decreases. Finally, when the diameter is larger than another critical size, the new nonuniform state becomes unstable, and a vortex enters the particle. Therefore, the presence of the new nonuniform state plays an intermediate role in the evolution from the quasiuniform state to the vortex state as the diameter increases.