Off-campus UNL users: To download campus access dissertations, please use the following link to log into our proxy server with your NU ID and password. When you are done browsing please remember to return to this page and log out.
Non-UNL users: Please talk to your librarian about requesting this dissertation through interlibrary loan.
First-Principles Calculations of Voltage-Controlled Magnetic Anisotropy and Spin-Orbit Torque in Magnetic Materials
Voltage-controlled magnetic anisotropy and spin-orbit torques are promising and efficient methods of switching magnetization in spintronic devices. In this dissertation, first-principles methods are used to study them in real material systems. First, the magnetic anisotropy in MgO-capped antiferromagnetic MnPt films and its voltage control are studied using first-principles calculations. The results show that the magnetic anisotropy can be widely tuned by adjusting the film thickness, particularly in Pt-terminated films. The linear voltage control coefficients are found to be large, indicating the potential of MgO-capped MnPt films as a versatile platform for magnetic memory and antiferromagnonic applications. Next, spin-orbit torques in a Mn2Au/heavy-metal bilayer are studied using the non-equilibrium Green's function (NEGF) technique. Spin-orbit coupling in the bulk of Mn2Au generates a strong fieldlike torquance, which is parallel on the two sublattices and scales linearly with the conductivity, and a weaker dampinglike torquance that is antiparallel on the two sublattices. Interfaces with heavy metal generate parallel dampinglike torques of opposite signs that are similar in magnitude to those in ferromagnetic bilayers and similarly insensitive to disorder. The dampinglike torque efficiency depends strongly on the termination of the interface and on the presence of spin-orbit coupling in Mn2Au, suggesting that the dampinglike torque is not due solely to the spin-Hall effect in the heavy metal layer. Interfaces also induce antiparallel fieldlike and dampinglike torques that can penetrate deep into Mn2Au. These results can help in the design and optimization of antiferromagnetic spintronic devices. Last, spin-orbit torques and their disorder dependence in an L11-ordered CuPt/CoPt bilayer are studied using the NEGF technique. The C3v symmetry at the interface gives rise to 3m torques which can enable field-free switching of perpendicular magnetization. It is found that 3m fieldlike torque accounts for 20% of damplinglike torque. Our results can be further used as input to study the magnetization dynamics using micromagnetics and provide insights into the mechanisms for spin-orbit torques in this system.
Fang, Wuzhang, "First-Principles Calculations of Voltage-Controlled Magnetic Anisotropy and Spin-Orbit Torque in Magnetic Materials" (2023). ETD collection for University of Nebraska - Lincoln. AAI30574191.