A Component-wise Model for Understanding Spin-Charge Interactions in Nanoparticle Solids Using Targeted Synthesis, Magnetometry, and Magnetoresistance

PART 1: NON-TECHNICAL SUMMARY At the heart of much of modern technology and materials science lies the challenge of understanding and controlling the interaction between an electron’s charge and its spin. This project, which is supported by the Solid State and Materials Chemistry program in NSF’s Division of Materials Research, targets that challenge by focusing on a phenomenon known as magnetoresistance (MR). For a magnetoresistant material, a magnetic field can be used to change the material’s electrical resistance. Unlike traditional MR devices that employ intricate layered structures as the active MR material, this project embraces a unique, simpler, and highly adaptable approach, namely leveraging advances in low-cost, high-purity magnetic nanoparticle synthesis and assemble them into MR-active hybrid composites. This method promises to be more fault-tolerant and tunable, enabling researchers to develop, test, and refine theories of MR and spin transport at an unprecedented pace. Furthermore, this project enhances the impact of its research through a commitment to transparency and accessibility in data management. In an era where data fuels discovery, the team will focus on data analysis and software development embedded in FAIR principles, building a culture of “open-source” research that is genuinely Findable, Accessible, Interoperable, and Reusable to the public funders who make the research possible. PART 2: TECHNICAL SUMMARY The research, which is supported by the Solid State and Materials Chemistry program in NSF’s Division of Materials Research, explores a nanoscale bottom-up approach to one of the most technologically important methods of electronic spin-charge interaction: magnetoresistance (MR). Instead of the traditional layered MR materials, the research team of Professor Jeffrey Rinehart at UC San Diego focuses on granular MR materials composed of nanoparticles synthesized with specific composition and magnetic phase requirements. By leveraging advancements in colloidal nanochemistry, unparalleled control over the magnetic structure of individual particles is obtained and thoroughly characterized, thereby allowing rigorous correlation with the MR behavior of composite material structures. This is the first time that researchers establish quantitative structure-function relationships between well-defined parameters: interparticle interaction strength, single-particle magnetic anisotropy, and particle volume. Elucidating these key factors influencing the MR behavior of the system allows mapping out the full landscape of MR response as multidimensional response function, providing a far more comprehensive characterization than has previously been attempted. Starting from the simple but important ferrite-based systems, research expands to high-performing magnetic materials with an ultimate goal of creating MR systems with adjustable field sensitivity and pseudo-spin valve behavior for a variety of sensing applications. The research includes an extensive data organization and modeling component with an emphasis on alignment with FAIR data principles and making data widely available for study. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.