Graduate Studies

 

First Advisor

Kirill D. Belashchenko

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Physics & Astronomy

Date of this Version

5-2024

Document Type

Dissertation

Citation

A dissertation presented to the faculty of the Graduate College of the University of Nebraska in partial fulfillment of requirements for the degree of Doctor of Philosophy

Major: Physics and Astronomy

Under the supervision of Professor Kirill D. Belashchenko

Lincoln, Nebraska, August 2024

Comments

Copyright 2024, Giovanni Gabriel Báez Flores. Used by permission

Abstract

This dissertation presents first-principles studies focusing on the effects of interfacial spin relaxation in metallic interfaces, interfacial intermixing on spin-orbit torques, and the effects of alloying on the transport properties of Fe|MgO|Fe magnetic tunnel junctions. Spin transport and spin-orbit torques are at the heart of phenomena in magnetic memory devices, such as tunnel magnetoresistance and magnetization switching. This work explores spin transport, spin-orbit coupling, spin-orbit torques, and tunneling magnetoresistance in a variety of materials and interfaces.

First discussed is the role of spin-orbit coupling at metallic interfaces by establishing a generalized magnetoelectronic circuit theory for normal metal (NM) interfaces, (NM|NM), and normal and ferromagnetic metal (FM) interfaces, (FM|NM). This theory expands on the concept of spin-mixing conductance by describing spin non-conserving processing. Particular emphasis is placed on the spin memory loss parameter, δ, and its relationship with spin-flip transmission and reflection probabilities. Secondly, this dissertation explores the impact of interfacial intermixing on spin-orbit torques in Co/Pt bilayers. Utilizing nonequilibrium Green's function techniques with supercell disorder averaging, the research shows how interfacial intermixing enhances both dampinglike and fieldlike torques, suggesting potential pathways for tuning these torques through interface engineering.

Lastly, this investigation examines the minority-spin Fe|MgO interface states, addressing discrepancies between density functional theory predictions and experimental observations. Introducing an empirical potential correction, the study shows how the correction affects the tunnel magnetoresistance in Fe|MgO|Fe tunnel junctions and explores the effects of Co and V alloying on the junctions Fe leads.

Overall, the research presented expands the understanding of interfacial spin transport by generalizing magnetoelectronic circuit theory in ferromagnetic multilayers, introducing methods to enhance spin-orbit torque in bilayers, and clarifying the role of surface resonances in Fe|MgO|Fe tunnel junctions. This work seeks to offer valuable insights for the advancement of spintronic devices like magnetic random-access memory (MRAM) devices.

Advisor: Kirill D. Belashchenko

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