Shape anisotropy-induced local incoherent magnetization: Implications for magnetic sensor tuning

Abstract

The geometry of magnetoresistive sensors based on thin magnetic films plays a crucial role in shaping their magnetization behavior and overall performance. This study investigates Wheatstone bridge sensors made with NiFe single-layer films (thickness: 10–40 nm; width: 20–60 μm; length: 500 μm) to analyze the impact of shape anisotropy on magnetization distribution. We observed domain images and sensor signals by applying a magnetic field with a constant direction and strength while varying the strength of a second magnetic field applied perpendicularly to the first. Wide-field Kerr microscopy revealed that magnetization reversal occurs locally and incoherently, with the degree of incoherence increasing in geometries with stronger demagnetizing fields. The demagnetizing field in rectangular-shaped thin films was calculated, revealing a sharp increase in field strength 3–4 μm from the bridge element edge when magnetized in the short-length direction, which results in localized magnetization behavior. The sensor signals were calculated and measured for various width-to-length ratios of the bridge elements and external magnetic field strengths. Results show that variations in sensor geometry and external magnetic fields can influence peak-to-peak voltage by up to 41 % and make significant hysteresis in the sensor signal. These findings provide valuable insights into optimizing the design and performance of magnetoresistive sensors for advanced applications. © 2025 Vietnam National University, Hanoi