Magnetic switching of single vortex permalloy elements

Abstract

Magnetic vortices play an important role in the switching behavior of micron- and submicron-sized ferromagnetic elements. We have prepared submicron permalloy elements by a combination of electron-beam lithography and liftoff technique on electron transparent membrane substrates. The magnetization reversal mechanism and the remanent magnetization configuration were observed by means of Lorentz transmission electron microscopy. In remanence, the investigated structures form a vortex configuration. In situ magnetizing experiments showed the possibility of adjusting the sense of magnetization rotation by introducing a slight geometric asymmetry to the otherwise circular nanostructures.

Chirality control via double vortices in asymmetric Co dots

“…24 Therefore, by simply analyzing the annihilation field, the vortex chirality can be determined. Additionally, as reported earlier by Schneider et al, 20 Interestingly, the reversal behavior of slightly larger asymmetric dots, 45nm thickness and 810 nm diameter, is strikingly different (Fig. 2).…”

“…2-panel (ii)], unlike that discussed in Ref. 20 . This buckling precedes the nucleation of two vortices from the rounded edge of the dot at a field of 260 Oe [ Fig.…”

“…Interestingly, asymmetric structures, e.g. nominally circular nanomagnets with a flattened edge 20,21 or triangularly shaped dots 22 , make chirality control possible. The broken symmetry leads to a preferred vortex nucleation site and subsequent chirality control.…”

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.…”

“…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.…”