The interfacial Dzyaloshinskii-Moriya interaction (DMI) in an in-plane anisotropic Pt(4nm)/Co(1.6nm)/Ni(1.6nm) film has been directly observed by Brillouin spectroscopy. It is manifested as the asymmetry of the measured magnon dispersion relation, from which the DMI constant has been evaluated. Linewidth measurements reveal that the lifetime of the magnons is asymmetric with respect to their counter-propagating directions. The lifetime asymmetry is dependent on the magnon frequency, being more pronounced the higher the frequency. Analytical calculations of the magnon dispersion relation and linewidth agree well with experiments.

We report the experimental observation of band gaps in a synthetic nanostructured magnonic crystal composed of two different magnetic materials. The sample, in the form of a one-dimensional periodic array comprising alternating Permalloy and cobalt nanostripes, has been fabricated using advanced lithographic techniques. Dispersion relations of spin waves in the magnonic crystal have been mapped by Brillouin spectroscopy. The center frequency and width of the band gaps observed are tunable by an applied magnetic field. Dispersion relations calculated based on the finite element method accord with the measured data.

Just as a photonic crystal is a periodic composite composed of materials with different dielectric constants, its lesser known magnetic analogue, the magnonic crystal can be considered as a periodic composite comprising different magnetic materials. Magnonic crystals are excellent candidates for the fabrication of nanoscale microwave devices, as the wavelengths of magnons in magnonic crystals are orders of magnitude shorter than those of photons, of the same frequency, in photonic crystals. Using advanced electron beam lithographic techniques, we have fabricated a series of novel bicomponent magnonic crystals which exhibit well-defined frequency bandgaps. They are in the form of laterally patterned periodic arrays of alternating cobalt and permalloy stripes of various widths ranging from 150 to 500 nm. Investigations by Brillouin light scattering and computer modeling show that the dispersion spectrum of these crystals is strongly dependent on their structural dimensions. For instance, their first frequency bandgap is found to vary over a wide range of 1.4-2.6 gigahertz. Such a functionality permits the tailoring of the bandgap structure which controls the transmission of information-carrying spin waves in devices based on these crystals. Additionally, it is observed that the bandgap width decreases with increasing permalloy stripe width, but increases with increasing cobalt stripe width, and that the bandgap center frequency is more dependent on the stripe width of permalloy than that of cobalt. This information would be of value in the design of magnonic crystals for potential applications in the emerging field of magnonics.

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Employing Brillouin spectroscopy, strong interfacial Dzyaloshinskii-Moriya interactions have been observed in an ultrathin Pt/CoFeB film. Our micromagnetic simulations show that spin-wave nonreciprocity due to asymmetric surface pinning is insignificant for the 0.8 nm-thick CoFeB film studied. The observed high asymmetry of the monotonic spin wave dispersion relation is thus ascribed to strong Dzyaloshinskii-Moriya interactions present at the Pt/CoFeB interface. Our findings should further enhance the significance of CoFeB as an important material for magnonic and spintronic applications. V C 2015 AIP Publishing LLC. [http://dx.