Thesis Defense: Caravaggio Caniglia, Karunadasa Group

“Halide perovskites as physical model systems”

In the past decade, extraordinary discoveries have been made in exfoliated 2D materials — famously, superconductivity in twisted bilayer graphene and giant magnetoresistance in graphene/chromium trihalide stacks. While these achievements highlight the potential for layered materials to both perform specialized functions in devices and address unresolved questions in physics, their impact is limited by the difficulty of achieving scalable synthesis. Exfoliation and deposition techniques for monolayer-thick materials have improved dramatically but are still expensive and technically demanding. The Karunadasa group’s previous work has shown that halide perovskite heterostructures can be fabricated using bulk self-assembly reactions in aqueous solution. I showcase the use of this synthetic methodology to direct the assembly of a magnetic model system, the diamond spin chain, in Cu–Cl perovskite heterostructures.

The sheets of a Cu–Cl perovskite are one of the canonical examples of 2D ferromagnetism. While considerable work has been dedicated to the study of monolayers of similar systems, most notably the chromium trihalides, interest in 2D Cu–Cl perovskites has been somewhat niche for several decades because they are not well-suited for mechanical exfoliation. I attempt to demonstrate that physical model systems can be isolated and systematically analyzed in materials based on the 2D Cu–Cl perovskite motif. To do so, I present analysis of a Cu–Cl perovskite heterostructure containing diamond spin chains and compare its magnetization, AC and DC magnetic susceptibility, and specific heat capacity to several heterostructures with slightly altered intergrowth layers between their perovskite sheets. Because these materials are cyrstallographically well-resolved and easy to synthesize, it is possible to verify structural alterations to the diamond spin chain motif and its distance from neighboring perovskite sheets using X-ray diffraction. Differences in magnetic behavior allow us to draw conclusions about structure/property relationships. To demonstrate the potential utility of fundamental structural and magnetic work in application-focused materials design, I show how similar synthetic chemistry can be adapted to fabricate 2D Cu–Cl perovskites that possess simultaneous piezoelectricity and antiferromagnetic order below 8 K.

Join via Zoom

Meeting ID: 935 149 1094

Password: 755152