Magnetic skyrmions are believed to be the promising candidate of information carriers in spintronics. However, the skyrmion Hall effect due to the nontrivial topology of skyrmions can induce a skyrmion accumulation or even annihilation at the edge of the devices, which hinders the real-world applications of skyrmions. In this work, we theoretically investigate the current-driven skyrmion motion on magnetic nanotubes which can be regarded as "edgeless" in the tangential direction. By performing micromagnetic simulations, we find that the skyrmion motion exhibits a helical trajectory on the nanotube, with its axial propagation velocity proportional to the current density. Interestingly, the skyrmion's annular speed increases with the increase of the thickness of the nanotube. A simple explanation is presented. Since the tube is edgeless for the tangential skyrmion motion, a stable skyrmion propagation can survive in the presence of a very large current density without any annihilation or accumulation. Our results provide a new route to overcome the edge effect in planar geometries.Ever since its experimental discovery, 1 the magnetic skyrmion, a chiral quasiparticle, 2,3 has been an active research area in condensed matter physics because of not only the potential for future spintronic applications such as skyrmion racetrack memories 4-6 and logic devices, 7,8 but also the fundamental interests. 9-13 In chiral magnets, skyrmions can be stabilized by the Dzyaloshinskii-Moriya interaction (DMI) of two types: 1,14-22 the bulk DMI and the interfacial one. The bulk DMI typically exists in noncentrosymmetric magnets, and can support the formation of Bloch-type (vortex-like) skyrmions, 1,15-18 while the latter one usually exists in inversion-symmetry breaking thin films, and can give rise to Néel-type (hedgehoglike) skyrmions. [19][20][21][22] Several methods have been proposed to drive the skyrmion motion, such as spin-polarized currents, 23 microwaves, 24 and thermal gradients, 25 to name a few. However, when the skyrmion is driven by an in-plane current via the spin transfer torque, the trajectory of its motion deviates from the current direction due to the intrinsic skyrmion Hall effect. 2,3,26-29 Furthermore, there exists a threshold current density above which skyrmions can annihilate at the film edge. 30 This edge effect strongly limits the speed of skyrmion propagation which is of vital importance for real applications. Several solutions have been proposed to overcome this problem. Zhang et al.proposed an antiferromagnetically exchange-coupled bilayer system, where the skyrmions move straightly along the current direction. 31 Upadhyaya et al. showed that the skyrmion can be guided in a desired trajectory by applying electric fields in a certain pattern. 32 More recently, Yang et al. discovered a novel twisted skyrmion state at the boundary of two antiparallel magnetic domains coupled antiferromagnetically, through which skyrmions with opposite polarities can transform mutually. 33 Under proper conditions, the doma...
In this work, deep levels present in n-type In 0.53 Ga 0.47 As hetero-epitaxial layers grown latticematched on n-type InP substrates by molecular beam epitaxy have been studied by deep-level transient spectroscopy (DLTS). Metal-oxide-semiconductor capacitors are employed, based on an Al 2 O 3 gate oxide. It is shown that a single, near mid-gap electron trap dominates the DLTspectra, whatever the surface pre-or post-gate oxide deposition treatment. At the same time, it is shown that the deep level parameters vary significantly from capacitor to capacitor and from wafer to wafer. Only after Forming Gas Annealing, a stable value for the activation energy of 0.39±0.01 eV is obtained. These results are tentatively interpreted in terms of antisite defects in the epitaxial layer, which form a family of related complexes with close deep-level parameters.
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