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Mouser Electronics White Paper nonvolatile magnetic storage. The GMR effect then enables the sensor to decode this stored state by detecting resistance changes, thereby determining the turn count. Figure 3: The GMR effect and its effected resistance. (Source: Chang et al. (2014) As shown in Figure 4, a GMR sensor uses the shape anisotropy of two structures: a circular domain wall generator (DWG) with low anisotropy and a narrow magnetic track with high anisotropy. When the magnetic field rotation between the DWG and the narrow track is zero, the structures exhibit homogeneous magnetization to the right (a). As the field rotates 90°, a domain wall appears at the entrance to the track (b). As the rotation increases to 120°, the domain wall moves into the track (c), and when the rotation reaches 180°, the domain wall reaches the end of the track, and the magnetization reverses (d). Figure 4: Domain wall generator with low shape anisotropy connecting to a narrow track with high shape anisotropy. (Source: Analog Devices) Figure 5 shows the DWG connected to a narrow track consisting of a nanowire that spirals outward to form a two-turn sensor. The arrows in the center of the figure show the direction of the fixed pinning layer (gray outline arrow), the direction of the external magnetic field (black outline arrow), and the direction of rotation of the external magnetic field (two-tone arrow). Figure 5: Extension of a narrow track to a two-turn spiral nanowire. (Source: Analog Devices) External connections to the narrow-track spiral nanowire include ground (GND), voltage supply (VDD), and four contact points (01, 02, 03, and 04). From these points, external circuitry can read resistance and infer the direction of the magnetic field (shown by the arrows superimposed along the nanowire track) in each segment of the track. The blue segments of the track denote low resistance, while the red segments denote high resistance. Figure 6 shows the effect of rotating the external magnetic field 180° clockwise. A domain wall appears at the inner ground contact, and the direction of magnetization in the track segment from the DWG to the GND connection flips. However, no changes propagate to the 01 contact position, and no electrical transitions occur at this time (with the current time denoted by the vertical bar in the bottom right of the figure). Figure 6: The appearance of a domain wall rotating the external magnetic field 180° clockwise. (Source: Analog Devices)

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