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(Color online) (a) Scanning electron micrograph of rings with a width of and an outer diameter of . (b) X-ray resonant magnetic scattering setup. Left and right circularly polarized (LCP and RCP) x-rays probe the magnetization along the applied field . At specular conditions , reflected intensities are measured as a function of incident energies and .
(Color online) Normalized XRMS signal as a function of applied field of (a) Co rings ( thick), (b) NiFe rings , (c) the Co layer of a NiFe ring structure, and (d) the NiFe layer of a structure. All samples are capped with Cu to prevent oxidation. Open symbols illustrate the magnetization path for declining external field, and full symbols indicate the opposite direction. Experimental data (squares) are compared to micromagnetic simulations (circles).
(Color online) Micromagnetic simulations of the spin configuration in the NiFe (left) and Co (right) layers in the pseudo-spin-valve-type ring structure at remanence. Antivortex states are formed, where the direction of the magnetization preferentially is pointing inward (I, II, and IV in NiFe; III in Co) and outward (III in NiFe; I, II, and IV in Co) to the rings. The external field was applied in the direction.
PEEM image of the NiFe layer of the multilayer rings exhibits diverse multi-domain structures at remanence. This suggests that imperfections in the rings strongly control the magnetic reversal.
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