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Scanning electron microscope images (recorded at a tilt angle of ) showing the one, two, and three ring structures. The lateral dimensions of the individual islands are W = 170 nm and L = 470 nm and the lattice parameter of the arrangement is a = 560 nm. The structures are spaced 3 apart to minimize dipolar coupling. A schematic illustration of the inner structure of the islands is also included.
XMCD images of the magnetic state of the ring structures recorded at ∼120 K. (a) The clockwise vortex ground state ordering of a one ring structure. The schematic below illustrates the determination of the magnetic state of each of the islands from the magnetic contrast. XMCD images showing the lowest energy levels of (b) a two ring structure and (c) a three ring structure.
The population of the four lowest energy levels determined from XMCD images. The ground state displays a higher probability compared to a random distribution, whereas higher energy levels display a lower probability. A total of 67 ring arrangements were imaged from which the state of a total of 54 ring structures could be identified.
The population of the ground state of the one ring structure and of the two lowest energy levels for the two and three ring structures (depicted in the graph). In all cases, the measured probabilities are higher than those expected from a random distribution. A total of 55 and 54 structures were imaged for the two and three ring structures, respectively, from which the state of a total of 39 and 31 structures could be identified.
XMCD images of a two ring structure showing the macrospins changing direction between the two energy minima. Over a period of 30 min, the state of the structure evolved from the lowest energy ground state to the second lowest energy level. Borders are drawn on to the images to highlight the location and arrangement of the islands. The macrospins which display a reversal of the magnetization direction are marked with a dashed white border.
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