Thin films of the high-temperature superconductor YBa 2 Cu 3 O 7 ؊ ␦ exhibit both a large critical current (the superconducting current density generally lies between 10 11 and 10 12 A m −2 at 4.2 K in zero magnetic field) and a decrease in such currents with magnetic field that point to the importance of strong vortex pinning along extended defects 1,2 . But it has hitherto been unclear which types of defect-dislocations, grain boundaries, surface corrugations and anti-phase boundaries-are responsible. Here we make use of a sequential etching technique to address this question. We find that both edge and screw dislocations, which can be mapped
New magnetic torque measurements on a high-quality Bi2Sr2CaCu20a; single crystal show that only a lower bound for the anisotropy parameter 7 > 150 can be given. For misorientations of the field H from the (a, b) plane larger than 0.5°, the results can be rescaled to magnetization M vs H. The behavior of M can be consistently described by a recent theory of Bulaevskii, Ledvij, and Kogan.
Despite the inefficiencies associated with current-induced spin torques, they remain the predominant mode of skyrmion propulsion. In this work, we demonstrate numerically that skyrmions can be transported much more efficiently with a voltage-controlled magnetic anisotropy (VCMA) gradient. An analytical model was developed to understand the underlying skyrmion dynamics on a track under the VCMA conditions. Our calculations reveal that the repulsive skyrmion-edge interaction not only prevents the skyrmion from annihilating but also generates most of the skyrmion propulsion. A multiplexed array of gate electrodes can be used to create discrete anisotropy gradients over a long distance, leading to the formation of a series of translatable skyrmion potential wells. Due to the strong confining potentials, skyrmions are transported at a 70% higher packing density. Finally, we demonstrated that this form of skyrmion propulsion can also be implemented on almost any 2D geometry, providing improved versatility over current-induced methods.
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