Spin-Correlated Optical Properties of Ferromagnetic Nanostructures

Abstract

The advancement of next-generation spin-based electronics will be aided by the development of materials whose optical responses are defined by spontaneous ferromagnetic ordering. Here, this dissertation leverages the chemical tunability of nanostructured materials to rationally design ferromagnets with spin-correlated optical responses, addressing the fundamental materials chemistry challenge that lies at the heart of achieving paradigm-shifting opto-spintronic technologies. Chapter 2 investigates the magnetic and magneto-optical properties of CsEuCl3 perovskite nanocrystals and thin films through a combination of photoluminescence and magnetic circular dichroism spectroscopies, elucidating the f–d nature of the CsEuCl3 optical properties and uncovering ferromagnetic ordering stemming from the same f–d origin. Chapter 3 develops new functionalities in the well-studied – yet recently overlooked – family of ferromagnetic Cr2+ 2D perovskites with magnon-assisted spin-flip transitions that provide an optical probe of magnetic ordering. This chapter expands the chemistry of these materials, focused on the previously unreported compositions PEA2CrX4 (PEA+ = phenethylammonium, X = Cl, Br). The steric bulk of the PEA+ cation dictates the overall chemical reactivity of these materials, imparting robust ambient stability to these otherwise famously hygroscopic compounds, and directing the formation of lateral PEA2Cr(Cl,Br) magneto-heterostructures in partial vapor-phase anion-exchange experiments. Chapter 4 transforms the broadband luminescence of the archetypal van der Waals ferromagnets CrX3 (X = Cl, Br, I) through dopant incorporation of spin-bearing Yb3+ narrow-line emitters. The Yb3+ magnetization is pinned to that of the CrI3 host through strong Yb3+–Cr3+ magnetic exchange coupling, evidenced via the Yb3+ circularly polarized luminescence. The Yb3+–Cr3+ magnetic exchange coupling arises through halide-mediated superexchange pathways that are highly dependent on the Yb3+-halide covalency. The influence of covalency in Yb3+:CrX3 is investigated through a host of photoluminescence experiments, identifying anomalously high Yb3+-iodide covalency in Yb3+:CrI3. In total, this dissertation accomplishes magnetic and magneto-optical tunability of metal-halide nanostructures across a range of compositions and morphologies, employing the chemical and spectroscopic toolboxes to design ferromagnets with spin-correlated optical properties.