Origin, criterion, and mechanism of vortex-core reversals in soft magnetic nanodisks under perpendicular bias fields

We studied dynamics of vortex-core reversals driven by circular rotating fields along with static perpen- dicular magnetic fields of different direction and strength. We found that the application of perpendicular fields Hp modifies the starting ground state of vortex magnetizations, thereby instigating the development of a magnetization dip mz,dip in the vicinity of the original core up to its threshold value, m z,dipp, which is necessary for vortex-core reversals, where p is the initial core polarization. We found the relationship of the dynamic evolutions of the mz,dip and the out-of-plane gyrofields hz, which was induced, in this case, by vortex-core motion of velocity , thereby their critical value relation crih z . The simulation results indicated that the variation of the critical core velocity cri with Hp can be expressed explicitly as cri/cri = /0pm z,dip , with the core size and the starting ground-state magnetization dip m z,dip variable with Hp, and for the values of cri and 0 at Hp=0. This work offers deeper and/or new insights into the origin, criterion and mechanism of vortex-core reversals under application of static perpendicular bias fields.