This differs from the 1D one- or two-component magnonic crystals studied earlier, where almost dispersionless branches appear well above the dispersive branches. Interestingly, the experimental magnonic band structure reveals spin wave modes with near-nondispersive behavior and having frequencies below that of the highly dispersive fundamental mode (see below). The measured phononic dispersion spectrum features a Bragg gap opening at the Brillouin zone (BZ) boundary, and a large hybridization bandgap, whose origin is different from those reported for other 1D-periodic phononic crystals. The dispersions of surface spin and acoustic waves were measured by Brillouin light scattering (BLS) which is a powerful probe of such excitations in nanostructured materials. It is also of interest to explore the effects on the magnonic dispersion when the material of one of the elements in a bicomponent magphonic crystal is a non-magnetic one. Hence, the phononic dispersion is expected to be significantly different from those of Py/Fe(Ni). Py and BARC were selected as materials for the high elastic and density contrasts between them. In this work, the magphonic crystal studied is a 1D periodic array of alternating Py and bottom anti-reflective coating (BARC) nanostripes deposited on an Si(001) substrate (abbreviated to Py/BARC). are small, being of the order of 0.5 GHz. Indeed the phonon bandgaps of the 1D and 2D structures measured by Zhang et al. In general, the phononic bandgap width increases with elastic and density contrasts. As the materials of the elements of these bicomponent arrays are both metals, namely either Py/Co, Py/Fe, or Py/Ni, the elastic and density contrasts between adjacent elements are rather low. experimentally studied these materials in the form of a two-dimensional (2D) chessboard-patterned array of cobalt and Ni 80Fe 20 (Permalloy, Py) dots, and one-dimensional (1D) periodic arrays of alternating Fe (or Ni) and Py nanostripes on SiO 2/Si substrates (henceforth referred to as Py/Fe(Ni)). Magphonic crystals were theoretically studied by Nikitov et al. Hence, they are potentially more useful technologically than either solely magnonic or phononic crystals which depend on a single type of excitation, namely magnons or phonons, as the respective information carrier. Although less well known than phoxonic materials, they too have promising application potential because of the possibility of the simultaneous control and manipulation of magnon and phonon propagation in them. Another class of metamaterials possessing dual-excitation bandgaps is magnonic-phononic or magphonic crystals. The present work builds a microscopic connection between electronic structure and giant anharmonic phonon scattering, providing new insights on the low lattice thermal conductivity of Mg 3Bi 2, and paves the way to design novel high-efficient thermoelectrics for application in energy recycling and refrigeration.Photonic-phononic crystals, also referred to as phoxonic crystals, are of great interest as their dual photonic and phononic bandgaps allow the simultaneous control of photon and phonon propagation in these crystals. Furthermore, we propose that the giant anharmonicty is associated with the asymmetric Bismuth 6s lone-pair electrons. In this work, the giant anharmonic phonon modes are experimentally observed via measuring temperature-dependent inelastic x-ray scattering (IXS) for Mg 3Bi 2 single-crystal, which is also verified by the anomalously large Grüneisen parameters and frozen phonon potential calculations. Understanding the microscopic thermal transport behavior and its correlation with bonding, lattice dynamics are critical to improve the thermoelectric performance and design new promising functional materials. However, the underlying physics of this low lattice thermal conductivity in a simple hexagonal crystal structure of Mg 3Bi 2 remain puzzling. Mg 3Bi 2-based materials exhibit high thermoelectric performance at ambient temperature benefitting from their low lattice thermal conductivity.
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