Graduation Year

2022

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Physics

Major Professor

Denis Karaiskaj, Ph.D.

Committee Member

Dario A. Arena, Ph.D.

Committee Member

Sagar Pandit, Ph.D.

Committee Member

Ashwin Parthasarathy, Ph.D.

Keywords

Ferrimagnet, Ferromagnet, Helimagnet, Magnetism, Pump-probe System

Abstract

Magneto-optic Kerr Effect (MOKE) is a very important method to investigate the magnetization ofmaterials with the polarization and intensity of light reflected from a sample. Both dynamic and static MOKE are performed to study the magnetic properties of thin films and bulk crystals in this research. For the static MOKE measurement, a solid state laser was used to probe the samples to generate a hysteresis loop by changing the external field from -0.8 T to 0.8 T. The magnet can be placed at an angle between 0 to 20 degree with respect to the sample surface to probe different sample magnetization orientations. In ultrafast MOKE, an amplified pulsed is used with 100 fs pulse duration and 1kHz repetition rate. With a femtosecond laser pulse, the ultrafast spin dynamics can be easily resolved. We measured a series of magnetic tri-layer thin films made of Pmd/Ru/Py and some single Pmd and Py samples in static MOKE setup and ultrafast MOKE setup. In tri-layer thin films, the thickness of middle layer(Ru) changes. While it varies, the exchange energy between Pmd and Py changes. The ultrafast MOKE can provide more details on the magnetization precession. Furthermore, the field dependence of the precession damping and double frequency behaviors can be observed. Hence, we can truly understand this ferromagnetic multi-layer samples, which can be used in applications such as recording media. Furthermore, we studied Cr1/3NbS2 , which is an interesting hexagonal chiral helimagnet with high crystalline anisotropy that has generated growing interest for numerous applications. Based on the detailed magnetization measurements of the high quality single crystal of Cr1/3NbS2, a comprehensive phase diagram is mapped over three magnetic field regions. The magnetization dynamics of these sample has not been studied before. Interesting results were revealed from temperature and field dependent ultrafast MOKE measurements which may help improve our understanding and its application in developing future magnetic devices. We also measured static and ultrafast Magneto-optic Kerr effect on the Rare-Earth/Transition (RE/TM) metal films. These materials can be used in ultrafast, all-optical switching, efficient and tunable THz emitters, domain wall spintronics, generation and manipulating of topologically protected non-co-linear spin textures and magneto-optical recording. These samples have an unusual effect called magnetic compensation and the temperature at which this effect occurs can be tuned by varying the RE/TM ratio. The magnetic moments of RE and TM layers change as temperature changes. At the compensation temperature, the sample magnetization reaches minimum. Using a vibrating sample magnetometer (VSM), temperature dependent magnetometry measurements were used to determine the magnetic compensation temperature. By measuring the static MOKE on different samples, we can determine whether the compensation temperature is above or below room temperature. We also measured samples under different temperatures in ultrafast MOKE setup and found some spin related effects. Some potential future developments and investigations are discussed in the thesis.

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