Enhancement of spin-wave nonreciprocity in magnonic crystals via synthetic antiferromagnetic coupling

Spin-wave nonreciprocity arising from dipole-dipole interaction is insignificant for magnon wavelengths in the sub-100 nm range. Our micromagnetic simulations reveal that for the nanoscale magnonic crystals studied, such nonreciprocity can be greatly enhanced via synthetic antiferromagnetic coupling. The nonreciprocity is manifested as highly asymmetric magnon dispersion curves of the magnonic crystals. Furthermore, based on the study of the dependence of the nonreciprocity on an applied magnetic field, the antiparallel alignment of the magnetizations is shown to be responsible for the enhancement. Our findings would be useful for magnonic and spintronics applications.

Nanostructured magnonic crystal with magnetic-field tunable bandgap

Most experimental investigations into magnonic bandgaps are based on structures composed of single-constituent magnetic materials. Here we report Brillouin and numerical studies of the spin dynamics of a bi-component magnonic crystal, viz. a one-dimensional periodic array of alternating permalloy and cobalt 150 nm-wide nanostripes. Our measurements, together with those for a similar crystal composed of 250 nm-wide nanostripes, suggest that for a stripe width ratio of 1:1, the bandgap width of such magnonic arrays increases with crystal lattice constant. The bandgap parameters are strongly dependent on external magnetic field. This magnetic-field tunability of the bandgap is expected to be a crucial property of devices based on magnonic crystals. The agreement between numerical calculations, based on finite element analysis, and the experimental data is generally good.