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NANOSCALE MAGNETIC FIELD SENSING WITH SPIN-HALL NANO-OSCILLATOR DEVICES

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2024-09-05
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Nanoscale magnetic field sensing is essential for many applications, including high-density magnetic storage readout, biomagnetic signal detection, and high resolution magnetic imaging. In recent years, people have proposed using magnetic nano-oscillators such as spin-torque nano-oscillators (STNOs) as alternative nanoscale magnetic field sensors, based on their ability to convert magnitude of magnetic field change into oscillation frequency change. However, the quantification of the sensor detectivity in such devices is still lacking. In this dissertation, we develop nanoscale magnetic field sensors based on a similar kind of magnetic nano-oscillators, spin-Hall nano-oscillator (SHNO) devices. We fabricate nanoconstriction-based SHNO devices using a Ni81Fe19/Au0.25Pt0.75 bilayer with different designs of the constrictions. In the first part of our work, we explore the possible synchronization in 4-constriction SHNO devices with the constrictions in-line and shifted by 30 degrees, both experimentally and numerically. The shifted design is to maximize spin wave overlap in the direction perpendicular to the external magnetic field. We observe synchronization in the device with shifted constrictions, but no global synchronization is identified in the device with in-line constrictions under the same magnetic field conditions. In the second part of our work, we study the temporal stability of nanoconstriction-based SHNOs and demonstrate their ability of quasi-DC magnetic field sensing up to kHz-scale frequencies under a bias field of 400 Oe in the sample plane. The magnetic field sensing is based on the linear dependence of SHNO oscillation frequency on the external magnetic field. We study two devices with 1 and 4 constrictions, respectively. Following the results from the first part, the chosen 4-constriction device has shifted design to facilitate synchronization. The detectivity of the 4-constriction device is as low as 0.21 μT Hz^(-1/2) at 100 Hz, with an effective sensing area of 0.31 μm^2. Our SHNO sensors combine good detectivity with small effective sensing area, with their detectivity outperforming other room temperature sensors with similar sub-micron effective sensing area. The nanoscale sensing area of the SHNO devices makes them interesting as local sensors, for example in scanning probe magnetometry.

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127 pages

Supplemental file(s) description: Magnetization dynamics for device with shifted constrictions at 1.8 mA, Magnetization dynamics for device with shifted constrictions at 1.4 mA, Magnetization dynamics for device with shifted constrictions at 1 mA, Magnetization dynamics for device with in-line constrictions at 1.8 mA, Magnetization dynamics for device with in-line constrictions at 1.4 mA, Magnetization dynamics for device with in-line constrictions at 1 mA.

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2023-08

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magnetic devices; magnetic field sensors; spin Hall effect; spin Hall nano-oscillators; spintronics

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Fuchs, Gregory

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Ralph, Daniel
Damle, Anil

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Applied Physics

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Ph. D., Applied Physics

Degree Level

Doctor of Philosophy

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Government Document

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dissertation or thesis

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