Vortex motion in chilarity-controlled pair of magnetic disks

Abstract

The authors investigate the influence of the vortex chirality on the magnetization processes of a magnetostatically coupled pair of magnetic disks. The magnetic vortices with opposite chiralities are realized by introducing asymmetry into the disks. The motion of the paired vortices are studied by measuring the magnetoresistance with a lock-in resistance bridge technique. The vortex annihilation process is found to depend on the moving directions of the magnetic vortices. The experimental results are well reproduced by the micromagnetic simulation.

Stochastic formation of magnetic vortex structures in asymmetric disks triggered by chaotic dynamics

“…2a. As can be seen in the images, the generated circularity c in individual disks is not always the same within repetitions, but exhibits a stochastic character, particularly in the disks of d ¼ 500 nm, which is in sharp contrast to the assumption in previously published literatures that a certain circularity would be reliably formed in such disks because of the asymmetric geometry [30][31][32] . Interestingly, although the vortices were formed under an identical sequence of field sweep from þ 1 kOe to 0, CCW circularities (c ¼ À 1) are predominantly generated in the disks within the array of d ¼ 200 nm, whereas CW circularities (c ¼ þ 1) are dominantly created in the disks with d ¼ 800 nm.…”

“…On the other hand, there is no clear preference for any given circularity in the array with d ¼ 500 nm. The transition of predominantly created circularity from c ¼ À 1 to c ¼ þ 1 by changing the interdisk distance from d ¼ 200 nm to d ¼ 800 nm is completely unexpected as a CW circularity has been reported to be formed in the same field sequence from þ 1 to 0 kOe in previous studies for the circularity control in asymmetric disks [30][31][32] . Micromagnetic simulations for the energies of CW and CCW vortex configurations show that the energy difference between CW and CCW states is very small (B10 À 32 J) and comparable to the level of computational errors in all arrays regardless of the interdisk distance.…”

“…A-priori, one would assume that only one type of circularity in asymmetrically shaped disks would be reliably selected as long as the direction of external fields for saturating and releasing the disks is fixed [30][31][32][33] . However, our results show that the final outcome of circularity depends on minute details of the dynamics in the initial stage of the formation process.…”

Simultaneous control of magnetic topologies for reconfigurable vortex arrays

“…It should be noted that the rotational sense of circularity selected by each field sequence in the disks within the array shown in Figure 2a is opposite to the one formed in an isolated disk with the identical field sequence. 24,26,27 Under the positive (negative) field sequence, CCW (CW) circularity is generated in the disks within the array, whereas CW (CCW) circularity is created in an isolated disk. 24,26,27 To understand the change in the type of created circularity between disks within the array and a single isolated disk, we considered the effect of the stray field on the vortex creation process.…”

“…Thus far, both static and dynamic studies on the control of vortex structures have been primarily dedicated to manipulation of either the c or p alone. 8,[21][22][23][24][25][26][27][28][29][30][31] A few attempts have been made to control both c and p, but these attempts have been conducted without repetition, meaning that only a single event of control has been investigated. 32,33 Therefore, reliability and repeatability for control of both topological features has not yet been addressed.…”