CAREER: Study of Degeneracy Breaking Effects and Emergent Phenomena in Heterostructures of Frustrated Antiferromagnets

Florida State University, Tallahassee FL

Investigators

Abstract

Non-technical abstract: Today's high tech society relies heavily on electronics such as computers, which use the movement of charge (electrons) to function. The electron has another property, its spin (i.e., rotational momentum). In most magnetic materials these spins are neatly arranged on a repeating pattern of atomic nuclei. In ferromagnets, the kind of magnets that decorate fridges, all these spins are aligned in the same direction, making the material magnetic with a well-defined north and south pole. The research team works on exotic magnets with atomic nuclei arranged in triangular patterns in which the spins cannot make up their minds about where to point. This allows the system to not adopt just one state but rather fluctuate between many available states. The "spin flips" associated with these fluctuations can be regarded as particles that have only a single magnetic pole. One of the major themes of this project is to investigate whether these spin flips can be used as information carriers in future generations of information technology, such as quantum computing. The research team synthesizes these exotic magnets in thin film form at Florida State University and the National High Magnetic Field Laboratory (NHMFL). By straining the thin film material the principal investigator tweaks the atomic positions, and the magnetic properties, which are studied using state-of-the-art facilities at the NHMFL and at national laboratories. This work is paramount in paving the way to a future in which devices based on exotic magnetic materials make use of spins, rather than charges, as information carriers. These research goals are integrated with undergraduate level curriculum development in materials synthesis to provide students at Florida State University with an education that will prepare them for the emerging advanced materials workforce. Outreach efforts include public lectures and middle school classroom activities that aim to increase (materials) science capital within the community. With these activities the principal investigator works to increase science awareness and interest in students and to empower them to make more informed decisions about their future career paths. Technical abstract: This project seeks to study ground state selection, emergent properties, and concomitant exotic excitations in geometrically frustrated systems as they are exposed to degeneracy breaking perturbations. Strong spin/lattice coupling is expected to lead to emergent ground states in structurally engineered films and heterostructures of frustrated antiferromagnets. The initial focus is on pyrochlore titanates, geometrically frustrated systems in which the Ising anisotropy leads to formation of a spin ice state showing only short range correlations. The spin ice state has been shown to host topological excitations that behave like magnetic monopoles. There is an enticing potential of harnessing topological excitations, such as monopoles, as novel types of information carriers. The project is aimed at characterizing how the spin ice physics, and the formation and dynamics of the monopoles, respond to external perturbations such as epitaxial strain. Furthermore, the application of strain in thin film samples unavoidably leads to a reduction in dimensionality, and the effect of such confinement on spin ice physics, which is predicted to be significant, is being investigated. Spin ice physics is also observed in spinel vanadates, poster materials for orbital physics in frustrated antiferromagnets. The PI utilizes epitaxial strain to tune noncollinear spin textures and stabilize a d-electron analogue of the spin ice state on the pyrochlore V sublattice in spinel vanadate thin films. The general approach for activities associated with this project can be described as, 1) systematic synthesis and structural characterization of strained thin films of frustrated antiferromagnets, 2) characterization of the magnetic properties, and associated noncollinear spin textures, using capacitive torque magnetometry measurements and elastic neutron scattering studies, and 3) development of the torque technique to include the ability to probe spin flip dynamics in spinel and pyrochlore thin films. 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.