Abstract
We studied the magnetization evolution in three-dimensional chiral nanostructures, including nanotubes and circularly curved thin films, by micromagnetic simulations. We found that in a nanotube skyrmions can be formed by broken of the helical stripes on the left and right sides of the nanotube, and the formation of skyrmions doesn’t correspond to any abrupt change of topological number. Skyrmions can exist in a large range of magnetic field, and the thinner nanotube has a larger field range for skyrmion existence. The configuration of a skyrmion in nanotubes is different from the one in thin film. From the outer to the inner circular layer, the size of the skyrmion becomes larger, and the deformation becomes more obvious. In circularly curved magnetic films with fixed arc length, there are three kinds of hysteresis processes are found. For the curved films with a large radius, the magnetization evolution behavior is similar to the case in two-dimensional thin films. For the curved films with a small radius, the skyrmions are created by broken of the helical stripes on the left and right sides of the curved film. For the curved film with a medium radius, no skyrmion is formed in the hysteresis process.
Highlights
We studied the magnetization evolution in three-dimensional chiral nanostructures, including nanotubes and circularly curved thin films, by micromagnetic simulations
The magnetizations on the left and right sides of the nanotube rotate to the z-direction, which narrows down the helical stripes at these positions, and the magnetizations whose orientation ia along the –z-axis are distributed mainly on the top and bottom of the nanotube (Fig. 1d)
The topological number Q jumps to about 4 when Hz = 1.01 T, which corresponds to the annihilation of four skyrmions that near the boundary, and the other four skyrmions annihilate at Hz = 1.14 T
Summary
We studied the magnetization evolution in three-dimensional chiral nanostructures, including nanotubes and circularly curved thin films, by micromagnetic simulations. It has demonstrated that curvature will induce two additional energies: geometrically induced-anisotropy energy and effective Dzyaloshinskii-Moriya interaction (DMI) energy[3,4,8] These additional energies excite many striking novel properties in three-dimensional curved magnetic thin films, wires, and nanotubes, such as magnetochiral effects[9,10], topologically induced magnetic patterns[11], and Spin-Cherenkov effect of spin waves[12]. It is known that skyrmions are rather peculiar topological magnetic structures and they have been observed in several classes of magnetic materials without inversion symmetry[13,14,15,16,17,18,19,20,21,22,23,24,25,26] Both DMI energy and anisotropy energy have an obvious effect on the stability of s kyrmions[14,27]. Those three-dimensional magnetic structures with complicated geometries and different sizes have been fabricated by various chemical and physical approaches[7,33,34,35], which may make our simulations be experimentally measured
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