Ryan McLaughlin Thesis Defense 05/05/17

Thesis Defense

Ryan McLaughlin

Friday, May 5, 2017
11:00AM (110 INSCC)

Title: Optical Studies of Thermal Spin Accumulation in Metallic Ferromagnets

As the miniaturization of electronic circuits approaches its fundamental limit, there is a need to find alternative methods to generate, manipulate, transfer and detect information and to reduce the energy needed for such operations. One approach to achieve this is to take advantage of the spin of electrons. Spin gives electrons their magnetic behavior, and using the spin in order to implement new functionalities in electronics is called “Spintronics”. One of the major obstacles to overcome in Spintronics is the development of a reliable “spin battery,” or a system that is analogous to a regular battery that generates a pure spin current on demand. One of the more promising avenues toward a functional spin battery is the Spin Seebeck Effect, which utilizes the interactions between charge carriers, lattice vibrations (phonons), and spin waves (magnons) in ferromagnetic materials to generate spin waves in response to a temperature gradient. However, the current methods that researchers use to electrically detect and quantify spin currents (based on the Spin Hall Effect) are susceptible to many undesirable magneto-thermoelectric artefacts. We resolve this dilemma with an all-optical, non-contact technique for detecting spin accumulation based on our interferometric magneto-optic Kerr effect (MOKE) microscope which is immune to thermoelectric artefacts and apply our technique to conclusively prove the existence of the Spin Seebeck Effect in magnetic Nickel-Iron alloys. Moreover, experimental geometries that are not possible with electrical detection are accessible to optical methods and a substantial anisotropy is found to depend on the magnetization being oriented in-plane or out-of-plane. I will discuss the microscopic mechanisms responsible for heat-to-spin current conversion and the implications of this anisotropy, along with future research avenues that are opened by our MOKE microscope technique.

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