CAREER: Novel Electronic and Magnetic Dynamics and Responses in Noncollinear Magnetic Materials

Colorado State University, Fort Collins CO

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports theoretical and computational research aimed at unraveling the conceptual and practical challenges associated with describing the magnetic order in the so-called noncollinear magnetic materials. Unlike the case for conventional ferromagnets and antiferromagnets, noncollinear magnetic order cannot be visualized as arrays of parallel and antiparallel microscopic magnetic moments. Traditionally noncollinear magnetism has been much less studied than ferromagnetism and anti-ferromagnetism, and has had limited applications. However, recently several noncollinear magnetic metals have been discovered to have surprising properties that could potentially lead to useful electronic and spintronic applications. This cohesive theoretical-computational project aims to identify new principles in the coupled electronic and magnetic dynamics of noncollinear magnets, new and unique response functions to external fields, and to predict new material systems which exhibit noncollinear magnetism. This project contributes to the search for new technological breakthroughs in systems with strong electron interactions. The strongly coupled spin and orbital degrees of freedom in noncollinear magnets may be exploited for efficient spin-charge conversion used in energy harvesting in different scales. The educational component of this project focuses on symmetry and big data, which are overarchingly important in today’s physics and materials science curricula. Through organizing a summer school on Principles and Applications of Symmetry in Magnetism, and redesigning a computational materials physics course to introduce concepts of machine learning, the PI will help local and national undergraduate and graduate students receive necessary exposure to these subjects and integrate them in their professional thinking. Given the multidisciplinary nature of this project, the undergraduate and graduate students involved in the research will also receive the essential training for embracing the “Quantum Leap” challenge in both fundamental science and technology. TECHNICAL SUMMARY Noncollinear magnetic order cannot be visualized as parallel or antiparallel magnetic moments arranged on a crystal lattice, as opposed to ferro- and antiferro-magnetic orders. Recent advancement of the study on such materials in spintronics and magnetotransport has been hindered by conceptual and practical challenges associated with the lack of vector-like order parameters and non-conservation of conduction electrons’ spin. This cohesive theoretical-computational project aims to address these challenges, through the following research thrusts: (1) Computational search for new noncollinear magnets guided by symmetry. Group-theoretic methods and the Landau theory of phase transition will be used to search for new noncollinear magnets in materials science databases beyond the very few known examples. (2) New response functions, functionalities, and experimental probes of noncollinear magnets. A hydrodynamic approach complemented by semiclassical wave-packet theory will be used to elucidate the unique conserved current in noncollinear magnets and its coupling to itinerant electrons. Quantum kinetic theory will be used to identify new response functions such as a counterpart of the giant magnetoresistance but without approximate spin conservation, and the magnetic spin Hall effect in terms of spin density polarization. A theory for using magnetic neutron scattering to detect local orbital magnetization will be formulated. This project contributes to the search for new technological breakthroughs in systems with strong electron correlations. The strongly coupled spin and orbital degrees of freedom in noncollinear magnets may be exploited for efficient spin-charge conversion used in energy harvesting in different scales. The educational component of this project focuses on symmetry and big data, which are overarchingly important in today’s physics and materials science curricula. Through organizing a summer school on Principles and Applications of Symmetry in Magnetism, and redesigning a computational materials physics course to introduce concepts of machine learning, the PI will help local and national undergraduate and graduate students receive necessary exposure to these subjects and integrate them in their professional thinking. Given the multidisciplinary nature of this project, the undergraduate and graduate students involved in the research will also receive the essential training for embracing the “Quantum Leap” challenge in both fundamental science and technology. 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.