Universal Criterion and Phase Diagram for Switching a Magnetic Vortex Core in Soft Magnetic Nanodots

Abstract

The universal criterion for ultrafast vortex-core switching between the up- and down-core bistates in soft magnetic nanodots is investigated by micromagnetic simulations along with vortex-core switching that occurs whenever the velocity of vortex-core motion reaches its critical velocity, upsilon cri = (1.66 +/- 0.18) gamma mean square root of Aex (e.g., upsilon cri = 330 +/- 37 m/s for Permalloy), with the exchange stiffness Aex and the gyromagnetic ratio gamma. On the basis of the universality of upsilon cri, phase diagrams for the vortex-core switching event and switching time with respect to both the amplitude and frequency of a circularly rotating magnetic field are calculated.

Symmetry breaking in the formation of magnetic vortex states in a permalloy nanodisk

“…With two possible orientations of c and p, four different ground states of a magnetic vortex can occur 7,8 . The magnetic vortex structure constitutes a fascinating topological structure for fundamental studies of nanoscale spin behaviour and offers great potential as a novel concept in data storage technologies [9][10][11][12][13][14][15] . A priori, one would expect the energy of the four states to be degenerate.…”

Coherence and modality of driven interlayer-coupled magnetic vortices

“…The LTEM images clearly show an absence of any static or highly coherent periodic motion. The lack of steady-state motion is interesting and could have several explanations, such as nonlinear interactions where, for example, the cores may reach critical velocities and reverse polarities 15,[38][39][40][41][42] . This clearly demonstrates that while the dipolar-coupled systems we present here still respond at characteristic frequencies, the collective modes can be convoluted and require further care when describing the resultant coupled vortex motion.…”

Spin-motive force due to a gyrating magnetic vortex

“…The magnetization in the core is perpendicular to the disc plane and can assume two different directions or polarities (up or down). It is known that when the core velocity exceeds a certain value (~250-300 m s − 1 ) 17 , the switching of the polarity becomes more frequent. Theory also predicts, for the current placement of the electrodes relative to the direction of the applied field, that there is no core polarity phase difference of the steady-state signals.…”