Magnetic triangular bubble lattices in bismuth-doped yttrium iron garnet

Abstract

Magnetic bubbles have again become a subject of significant attention following the experimental observation of topologically nontrivial magnetic skyrmions. In recent work, tailoring the shape of the bubbles is considered a key factor for their dynamics in spintronic devices. In addition to the reported circular, elliptical, and square bubbles, here we observe triangular bubble domains in bismuth-doped yttrium iron garnet (Bi-YIG) using Kerr microscopy. The bubble domains evolve from discrete circular to latticed triangular and hexagonal shapes. Further, the orientation of the triangular bubbles in the hexagonal lattices can be flipped by decreasing the magnetic field. The sixfold in-plane magnetic anisotropy of Bi-YIG(111) crystal, which is presumably the mechanism underlying the triangular shape of the bubbles, is measured as 1179 erg/cm3. The study of the morphologies of topologically trivial bubbles in YIG offers insight into nontrivial spin textures, which is appealing for future spintronic applications.

Topological Equivalence of Stripy States and Skyrmion Crystals

“…The physics reported here occurs in the bulk and should not depend on the boundary conditions. This is also what is observed in experiments . However, it is known that helical spin structures ending at a sample edge can be very complicated.…”

“…Q = 50 holds throughout 180 ns, and the morphology of the final states is similar to those at zero temperature for all films, as shown in Figure b. However, one distinct difference is that skyrmion surfaces are more irregular and rough at finite temperatures, agreeing with experiments, which may be understood from the negative skyrmion formation energy. Negative formation energy means negative surface tension such that such a surface can hardly resist external perturbations and deformations.…”

“…This is also what is observed in experiments. 54 However, it is known that helical spin structures ending at a sample edge can be very complicated. Skyrmion numbers of such spin textures are usually not integer.…”

In-plane spin excitation of skyrmion bags

“…Magnetic skyrmions, as topologically protected spin structures characterized by topological charges, have been widely studied in recent years. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Skyrmions have the characteristics of small size, topological protection, and low drive current density, which are conducive to the technical applications in high-density data storage equipment and low-energyconsumption spintronic devices. [18][19][20][21][22] In particular, the theoretical application of skyrmions has been extended to antiferromagnetic skyrmions, including racetrack memories, logic devices, spin nano-oscillators, and other promising spintronic devices derived from no spin Hall effect, zero stray field, and ultra-fast magnetization dynamics.…”