Overview: A fundamental investigation of the effects of controlled disorder and reduced symmetry on patterned thin-film metamaterials is proposed. Attention is focused on a new class of artificial magnetic quasicrystals that exhibit geometric frustration and complex spin ice behavior. Ferromagnetic resonance, static magnetization and numerical simulations will characterize spin wave excitations, frustration and possible phase transitions among spin ice phases, as driven by both temperature and magnetic field. The unique temporal coherence and phase sensitivity of X-ray photon coherent scattering (XPCS) will enable the first studies of magnetic relaxation and nonequilibrium dynamics of spin ices over a broad interval of field, temperature and time scales (10-3 to 103 s). Direct nanoscale imaging techniques (coherent X-ray scattering, magnetic force microscopy (MFM) and scanning electron microscopy with polarization analysis (SEMPA)) will characterize equilibrium magnetic textures and topological defects of spin ices of various topologies for comparison to dynamical data and numerical simulations. Intellectual Merit: The program addresses the following questions: What magnetic behaviors are inherent consequences of periodicity or disorder? How can similarities and differences in the behavior of randomly disordered and periodic systems be compared and understood? The signature long-range order without periodic translational symmetry of quasicrystal tilings places them in a unique niche of intermediate disorder between periodic crystals and amorphous materials. Bulk magnetic quasicrystals exhibit striking physical properties and frustration, but they are difficult to grow and characterize, and are known to adopt spin-glass, rather than long-range magnetic order. The proposed program therefore takes advantage of recent advances permitting nanofabrication of FM thin films into “artificial quasicrystals” whose spin wave excitations and reversal can be systematically controlled via tiling design. A first study of the effects of quasicrystal symmetry on cooperative interactions, frustrated dynamics and equilibrium ground state for this novel class of metamaterials is proposed. Aperiodic, long-range-ordered lattices based on Fibonacci distortions of periodic Bravais lattices will enable complementary studies of the effects of continuously variable aperiodicity on magnetic reversal, dynamics and spin ice behavior. The program will pursue spin wave localization due to controlled lattice disorder, and finite-size scaling behavior of physical observables in patterned films having variable topology, size and order. Recent XPCS experiments will be extended to determine precise conditions under which modest applied magnetic fields are observed to control transfer of orbital angular momentum to a soft X-ray “vortex beam” resonantly scattered from suitably designed artificial spin ices. Broader Impacts: Graduate and undergraduate students will receive instruction within an integrated program of in-house thin film deposition and patterning, and numerical simulations. Advanced physical and structural characterization includes broad-band FMR, static magnetization, X-ray reflectometry and AFM. Very few laboratories can provide such a broad program of research tools and skills. We will provide precision-patterned thin films for collaborative soft X-ray scattering, MFM and SEMPA experiments at Lawrence Berkeley, Argonne National Labs, and NIST (Gaithersburg), which will provide opportunities for visiting graduate students to work with postdoc
|Effective start/end date||6/1/15 → 5/31/18|
- National Science Foundation (DMR-1507058)
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