EXPERIMENTAL AND THEORETICAL INVESTIGATIONS OF NOVEL 2D MAGNET HETEROSTRUCTURES AND MAGNETIC THIN FILMS

Author

Stephen Hofer, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2023

Degree Name

Doctor of Philosophy

Department

Physics, Applied

First Advisor

Mazumdar, Dipanjan

Abstract

Since the first usage of magnets as navigation tools, magnetism has been an integral part of human technology. As such, with increased demand for more sophisticated technologies, the need to understand magnetism and its applications has also increased. In modern times, the focus of new technologies is on scalability, or how things behave on the smallest scales. To this end it is necessary to understand the fundamental and practical behaviors of magnetic materials at this limit. Recent discoveries in the field of true 2D magnets and the field of topological matter demands investigation of the intersection between these two fields. In the first part of this work a theoretical analysis of the topological behavior of magnon bands in CrI$_3$-like magnetic heterostructures is carried out. This analysis revealed a rich topological phase space wherein topological phase boundaries correspond to abrupt jumps in the thermal Hall conductance of the system, reminiscent of the quantum anomalous Hall effect. Additionally these systems showed distinct and repeating features between heterostructures with an even number of layers and those with an odd number of layers, making it theoretically possible to distinguish between the two based on the behavior of the thermal Hall conductance. Additional work was done on applications of magnetic thin film toward the field of spintronics. Spin-based magnetic random-access memory (MRAM) has a particular advantage over current electronic technology in its intrinsic non-volatility. Additionally, current MRAM devices that use spin-transfer torque can be improved by finding materials with high intrinsic perpendicular magnetic anisotropy which do not rely on interfacial-perpendicular anisotropy. To this end an investigation of the substrate dependent crystallinity of the Heusler alloy \Heu was performed using in-plane x-ray diffraction. By studying how the growth and orientation of the Bragg peaks ((200) and (002)) that correspond to the primary crystal axes, (a-b axes and c axis, respectively) it was determined that lattice matching and substrate play a large role in the formation of crystal plane orientations, potentially shining light on how these growth modes can influence the magnetic anisotropy of the films.