Synthesis and characterization of frustrated magnets as thin films

Abstract

Magnetic frustration, caused by contradictory competing interactions, leads to exotic emergent behavior in materials. The concept of frustrated magnetism is connected to quantum spin liquids, high-temperature superconductivity, anyon quasiparticles, topological transport, and more. Though most investigations of frustrated magnets focus on bulk crystals, thin films are more practical for device fabrication and provide unique pathways to tune or enhance behavior. Thin film frustrated magnets allow us to probe fundamental interactions within materials and have the potential to transform next-generation computing and information transport. Using reactive-oxide molecular beam epitaxy, I explore frustrated magnets as thin films through two different material systems: hexagonal ABO3 and pyrochlore A2B2O7. With the first thin films of quantum spin liquid candidate TbInO3, we explore how frustrated magnetism and improper ferroelectricity are modified from their bulk behaviors and measure anomalous high temperature spin transport. From the pyrochlore titanates, I synthesize the some of the earliest reported thin films of Y2Ti2O7, Tb2Ti2O7, Yb2Ti2O7, and Gd2Ti2O7. We find that changes in stoichiometry in thin film Tb2Ti2O7 lead to the formation of distinct defects which serve to reduce the frustration within the pyrochlore quantum spin liquid candidate. Further, we examine a coincident change in magnetic anisotropy, ferromagnetic hysteresis, and strain as a function of thickness down to the ultrathin limit in the first reported thin films of ferromagnetic insulator Y2V2O7. I also discuss the surprising growth of high quality epitaxial thin films of Y2Ti2O7 on quartz substrates, which may enable topotactic chemical modification of pyrochlore thin films. Finally, I explore how the precision of molecular beam epitaxy allows an exploration of pyrochlore properties at sub-unit-cell thicknesses with superlattices.