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. 2016 Feb 2;16(3):1626–1630. doi: 10.1021/acs.nanolett.5b04444

Figure 2.

Figure 2

A single tap near an isolated vortex attracts the vortex, independent of vortex polarity, enabling excellent control over vortex location. (a) Left and center, two noncontact images of the same vortex before and after tapping the sample once to the left of the vortex. The keyhole shape of an isolated vortex imaged by the SQUID results from the convolution between the magnetic field lines of the vortex and the shape of the SQUID’s pick-up loop (see Supporting Information for further discussion). Right, difference between the two images. The vortex moved in the direction of red (old) to blue (new). (b) A series of differential images illustrating the change in vortex location before and after a contact event (tapping). Images were obtained by subtracting consecutive scans. The cartoon above the images shows the position of the contact points (X) relative to the initial location of the vortex (green circle). Taps were spaced by 300 nm and approached the vortex from the left. In effective taps, the vortex moved toward the contact point. The scanned region was not shifted as the vortex moved. (c) Representative differential images taken from a full tapping sequence. Tapping was carried out at various orientations around a vortex within ∼1 μm. The tapping force was 1 μN. The location of the contact point is illustrated above each image (X) with respect to the vortex position prior to the tap (green circle) and after the tap (dashed circle). The scale bar on the illustrations marks the distance and direction of movement where D = 0.76, 1.4, 1.6, 1.2, 1.85, 1.4, 0.95, and 0.8 μm, respectively. Images were taken from the same vortex except for the last one, which was taken from a different vortex with opposite polarity. Note that for the opposite vortex (the last in the series), red (blue) represents the new (old) location. Vortices move toward the contact point regardless of vortex polarity. (d) Vortex configurations before and after we moved one vortex (circled) by 0.95 mm, while the locations of the other vortices did not change. (e) Vortex configuration after we moved vortices to form letters, showcasing the controllability of the technique.