Generation of local magnetic fields at megahertz rates for the study of domain wall propagation in magnetic nanowires
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(a) Schematic cross section of the device showing two levels of copper wiring layers labeled as M1 and M2 (dark and pale blue rectangles are ). The cross-section of the Cu lines are shown as rectangles (orange). An SiCHN (N-Blok) dielectric layer (green rectangle) is used on top of M2 to create an ultra smooth surface on which the permalloy nanowires are fabricated. A nanowire is shown as a rectangular shape (red) on top of the SiCHN layer. The darker rectangle within the nanowire (dark blue) represents a magnetic domain. The copper lines are oriented at 90° to the length of the permalloy nanowire so that the fields generated by these lines are oriented along the nanowire. (b) The Cu lines can be seen in this optical image of the top side of the device through the thin N-Blok layer. The M1 line and the M2 lines (with various widths) in this particular device are drawn in (a) for guidance. Note that also shown in this device are copper loops for detection of inductive voltage signals. The CMP process requires even fill with metal and dielectric: the arrays of copper dots seen in the image are fabricated for this purpose. On top of the N-Blok layer are the permalloy nanowire ( wide) and three electrical contact pads (only the left 2 are used here). (c) A high resolution cross-section scanning electron micrograph of part of a chiplet. Horizontal and vertical scales are shown at the bottom of the figure.
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[(a) and (e)] Time evolution of the DW injection field generated by M2 [the particular M2 line is indicated in Fig. 1(b)]. [(b) and (f)] Sequence of global fields generated by M1 used to drive the DW and to set/reset the magnetization of the nanowire ( and ). [(c) and (g)] Time evolution of at . [(d) and (h)] Dependence of at and at versus . (a)–(d) correspond to dynamic propagation of the DW in which is applied during the DW injection, whereas (e)–(h) correspond to static propagation of the DW in which is applied after the DW injection pulse is completed. (black lower curve), (red middle curve), and (green upper curve) in (a)–(d), (black lower curve), (red middle curve) and (green upper curve) in (e)–(h).
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Influence of current on dynamic propagation of DW. versus when (red open and closed circles), (black open and closed squares) and (green open and closed triangles). The current is simultaneously applied with the drive field. Data are shown for (a) tail to tail DWs (open symbols) and (b) head to head (closed symbols).
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