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Optimizing Magnetic Nanostructures and Microstructures for Ultrahigh-Sensitivity Magnetoresistive Sensors

Thesis Defense

2:00 pm–3:30 pm
Jorgensen Hall Room: 207
Physics Department, (402) 472-2770,
Yi Yang will defend his thesis, “Optimizing Magnetic Nanostructures and Microstructures for Ultrahigh-Sensitivity Magnetoresistive Sensors” via Zoom.

Join Zoom Meeting: Meeting ID: 93178133486

Magnetic tunnel junction (MTJ) based magnetoresistive sensors have shown great potential for application in biomedical measurement, flexible electronics, grid monitoring, nondestructive evaluation, autopilot, etc. owing to their strengths such as the high sensitivity, compact size, low power consumption, low cost, and capability to function at room temperature. In my dissertation, the magnetic nanostructures and microstructures of MTJ based magnetoresistive sensors are optimized for ultrahigh sensitivity of magnetoresistive sensors at room temperature. Firstly, it is demonstrated that even with the total magnetic thickness being several micrometers, laminated magnetic films can exhibit significantly reduced coercivity and saturation field compared to single-layer films with the same total magnetic thickness. Secondly, an integrated structure that connects micro magnetic flux concentrators (MFC) and MTJs is designed and studied, where laminated micro MFCs are utilized. And with external MFCs of centimeter scale added, a world-leading sensitivity as high as 4.71×103 %/Oe (4.71×104 %/mT) is demonstrated at room temperature. Thirdly, an optimized structure that combines a new layer structure of MTJ, where free layers are slightly pinned by antiferromagnetic layers in a direction perpendicular to the sensing direction, with the novel integrated structure is studied for improved overall performance of MTJ based magnetoresistive sensors. It is demonstrated that in the optimized structure, the magnetic anisotropy of the free layer can be tuned, and the fine-tuned magnetoresistive sensor exhibits reduced hysteresis, which results in improved reversibility and linearity, and a sensitivity as high as 3.82×103 %/Oe (3.82×104 %/mT). In addition, a simple and practical ac modulation method to reduce the hysteresis in magnetoresistive sensors is demonstrated. It is shown that with a suitable ac modulation magnetic ?eld that is applied along the sensing direction, the hysteresis in the sensors can be reduced to a negligible level. The progress achieved in this dissertation paves the way for the development of room-temperature ultrahigh-sensitivity magnetoresistive sensors for femtotesla magnetic field measurement.

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This event originated in Physics.