Date of Award
8-1-2026
Degree Name
Master of Science
Department
Physics
First Advisor
Mazumdar, Dipanjan
Abstract
The magneto-optical Kerr effect (MOKE) occurs when polarized light is reflected from a magnetized surface, causing changes in polarization angle (called Kerr rotation) and its state (linear vs elliptical, for example). In a simple version, MOKE measurement involves measuring the intensity of the reflected beam off the surface of a sample as an external magnetic field is swept through it. We record a change in the reflected intensity when the magnetization of the material changes. While easily measurable using modern electronics methods, the Kerr rotation is minimal, only of the order of milliradians (~0.1 deg), and is a characteristic of the magnetic material. Several parameters control the Kerr effect, including the incident polarization state, angle of incidence, and the magnetic field. During the past two years, we developed a variable-angle polarizer method to accurately estimate Kerr rotation and investigated longitudinal MOKE behavior using a custom-built experimental setup equipped with a manually rotated polarizer, an optical chopper, a lock-in amplifier, a wollaston prism, and two detectors. Data is obtained on a standard Cobalt magnetic thin film. By recording the s and p intensity of the reflected beam, we show that the Kerr effect is strong only for specific polarization states, and the Kerr rotation from a single measurement may lead to significant uncertainties, if not unmeasurable. Instead, the variable-angle polarizer measurements developed here can provide a reliable measurement of Kerr rotation. Using a cobalt thin film as a sample, we calculated the Kerr rotation for p-polarization to be 0.46 mrad and 0.66 mrad for s-polarization. Such values are in excellent agreement with the expected values.
Access
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