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 perpendicular magnetic fields of different direction and strength. We found that the application of perpendicular fields H p 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,dip cri ∼-p, 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 υ, thereby their critical value relation υcrihz cri. The simulation results indicated that the variation of the critical core velocity υcri with Hp can be expressed explicitly as υcri / υ cri 0 = (ρ/ ρ0) | -p- m z,dip g |, with the core size ρ and the starting ground-state magnetization dip m z,dip g variable with H p, and for the values of υ cri 0 and ρ0 at H p =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.open7