Selective domain wall depinning by localized Oersted fields and Joule heating
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[(a)–(d)] Schematic of a shift register in which domains are moved by using thermally activated DW traps. (a) The colors yellow and blue correspond to different magnetization directions. (b) A wire with periodically arranged notches exhibits different domain configurations between the traps. By applying a field [arrow in (b)] and heating one specific notch (red dot) the DW can be selectively depinned at this notch. (c) By heating a different notch and applying a field in the opposite direction [arrow in (c)], the DW is depinned at that notch and is caught at the next notch. Thus the domain is displaced one step forward (d) using this slip-stick motion (Ref. 7). (e) Optical micrograph of the sample. The bright wire is Py and the dark wires are Au. (f) In this schematic, the relevant sample features are shown. The DW is placed in the magnetic Py half ring. The central Au wire is used for current pulses and the four outer Au wires are used for the MR measurement [central Au wire and voltage contacts are shown in (f)]. The different positions of the DWs are indicated by numbers 1–5.
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(a) MR measurement at 4.3 K as a function of the angle of the saturation field (as detailed in Ref. 9). The DW positions are labeled by numbers, which correspond to those in Fig. 1. The corresponding DW positions are indicated in the schematics above. In the field direction range between and , we find that the wall can sit either at position 1 or 2 with a certain probability, which means that if the measurement is repeated for these angles, the resistance can be either high or low. For a single measurement as shown in (a), this results in the apparent noise between and , and to obtain reliable results, this angle range is not used in the later measurement. (b) Temperature dependence of depinning fields for a positive field (black squares) and a negative field (green dots) for the DW placed at (position 4). The red line is a fit curve using the model of Kurkijärvi (Ref. 10).
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DW propagation fields for different applied fields and current pulses for DWs positioned originally at [position 3, (a)] and [position 2, (b)]. The DW motion direction due to the external field is indicated by the blue arrows, and the direction due to the Oersted field is indicated by the yellow arrows. (a) Positive field: the black diamonds indicate the first displacement from position 3 to position 4. The orange disks indicate a DW motion from position 4 to 5. The pink down triangle indicates a displacement from position 3 to position 2. The data in (a) negative field show the corresponding results for a reversed applied field. Turquoise squares indicate the displacement from position 3 to 2, blue up triangles indicate the displacement to position 1, and the red star is the displacement from position 3 to 4. (b) shows the result for a DW placed at . The schematics below the graphs visualize the DW motion direction in the sample.
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