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Mesoscopic thin-film magnetic rings (invited)
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Image of FIG. 1.
FIG. 1.

Plan-view and side-view scanning micrographs of (a) and (b) arrays of Co circular rings, (c) elliptical rings, (d) elliptical rings, and (e) and (f) pseudo-spin-valve elliptical ring device with six nonmagnetic contact wires.

Image of FIG. 2.
FIG. 2.

OOMMF simulation (left) and MFM image (right) of (a) an onion state, (b) a twisted state in a circular ring. The data correspond to Co rings with a outer diameter of 520 nm and a width of 110 nm. Colors indicate the domain walls. Schematics within the micromagnetic calculation show the overall magnetization directions. An approximate outline of the rings is superposed on the MFM images. Adapted from Ref. 9.

Image of FIG. 3.
FIG. 3.

(a) Micromagnetic simulation using LLG of the vortex-type domain wall in a 250-nm-wide NiFe ring. (b) Corresponding Fresnel image showing the domain-wall structure. The two dark fringes at the edge of the ring indicate where the two opposite magnetization directions overlap. The bright spot indicates a vortex structure as in the simulation.

Image of FIG. 4.
FIG. 4.

Data for a diameter, 45-nm-thick NiFe ring, showing the number of consecutive field cycles over which the same vortex circulation direction is maintained. The lines represent a geometric probability distribution which fits the data well. The probability of a change from clockwise counterclockwise vortex on a given field cycle is 0.17, and 0.12 for the counterclockwiseclockwise change (Ref. 29).

Image of FIG. 5.
FIG. 5.

(a) MR measurements of a -long NiFe ellipse with an aspect ratio (major/minor axis) of 2, with the magnetic field applied along the major and minor axes. AMR is defined as the resistance change divided by the minimum resistance. The major and minor loop data are offset vertically for clarity. The inset SEM shows the electrical configuration. (b) Simulated MR of the NiFe ellipse with the field applied along the major and minor axes based on the micromagnetic configuration of the ring and the contact geometry shown. Only half the calculated loops are shown.

Image of FIG. 6.
FIG. 6.

Hysteresis loops of elliptical rings with major diameter, minor diameter, and a width of . (a) as deposited, in which the exchange bias direction is along the major axis of the ellipse. The major axis is the easy axis. (b) After a field cooling that sets the exchange bias direction perpendicular to the major axis, the minor axis is now the easy axis.

Image of FIG. 7.
FIG. 7.

Giant magnetoresistance curves for elliptical and circular PSV rings. The applied field was swept from positive to negative saturation. The insets show corresponding scanning electron micrographs and schematics of the contacts used for the measurements. (a) GMR curves for applied field directions along 0° (full circles, vertical on page) and 90° (open circles, horizontal on page), corresponding to an elliptical PSV ring with a -long axis, -short axis, and a width of 130 nm. (b) GMR curves of a circular PSV ring with an outer diameter of and a width of 200 nm, for applied fields along the 0° and 90° directions.

Image of FIG. 8.
FIG. 8.

Giant magnetoresistance loops of a PSV elliptical ring with a long axis, a short axis, and a width of 200 nm. The applied field was along the 0° direction and the measurements correspond to different contact configurations for the current and voltage leads. Filled circles: current contacts A and D, voltage contacts B and C. Open circles: current contacts B and F, voltage contacts BC and E.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Mesoscopic thin-film magnetic rings (invited)