Magnetic properties of ABC-stacked kagome antiferromagnets through the lens of novel Mn3Ge thin films

Abstract

In this thesis, the magnetic properties and transport behaviours of novel, tetragonally distorted epitaxial thin films of Mn3Ge are explored. Mn3Ge belongs to a class of materials that exhibit non-collinear antiferromagnetic spin configurations that give rise to unique electrical transport phenomena, such as the anomalous Hall effect (AHE), which can be utilized in spintronics applications. The films of this study were deposited on insulating 4H-SiC(0001) substrates, with successful crystallization leading to a unique tetragonally distorted L12 phase instead of the expected hexagonal D019 form. Magnetometry and magnetotransport measurements revealed complex magnetic behaviors including a large saturation magnetization, complicated ferrimagnetic characteristics, and unusual AHE contributions. These results pointed to the need for modifications to the phenomenological model used for other L12 structures, such as Mn3Ir and Mn3Pt. A symmetry analysis of all possible nearest-neighbour and same-site bilinear magnetic interactions in the L12 system uncovered an anisotropic exchange term that has been previously overlooked. This term is potentially important for understanding the canting of the spin structure away from a coplanar configuration. It was found that a relatively simple modification to the nominal cubic model that accounts for the tetragonal distortion of the films does a good job of qualitatively reproducing many of the observed magnetic behaviours. The study concludes with several potential avenues for future work, including further characterization of the magnetic configuration, optimization of film growth processes, and investigation of the material’s electronic band structure, which could deepen the understanding of its intriguing transport properties. This work advances the field of antiferromagnetic and ferrimagnetic spintronics and offers insights into the development of robust magnetic bits with low stray field and potentially high switching speeds.