Spin-Wave Channeling in Magnetization-Graded Nanostrips

Abstract

Magnetization-graded ferromagnetic nanostrips are proposed as potential prospects to channel spin waves. Here, a controlled reduction of the saturation magnetization enables the localization of the propagating magnetic excitations in the same way that light is controlled in an optical fiber with a varying refraction index. The theoretical approach is based on the dynamic matrix method, where the magnetic nanostrip is divided into small sub-strips. The dipolar and exchange interactions between sub-strips have been considered to reproduce the spin-wave dynamics of the magnonic fiber. The transition from one strip to an infinite thin film is presented for the Damon-Eshbach geometry, where the nature of the spin-wave modes is discussed. An in-depth analysis of the spin-wave transport as a function of the saturation magnetization profile is provided. It is predicted that it is feasible to induce a remarkable channeling of the spin waves along the zones with a reduced saturation magnetization, even when such a reduction is tiny. The results are compared with micromagnetic simulations, where a good agreement is observed between both methods. The findings have relevance for envisioned future spin-wave-based magnonic devices operating at the nanometer scale.

Spin‐Wave Optics in YIG Realized by Ion‐Beam Irradiation

“…Since FIB irradiation can continuously tune n eff of a magnetic film by changing the filling factor of an image in pixel space, we can create a magnetization landscape of arbitrary shape, including a GRIN lens [ 15 ] or GRIN fibers. [ 32 ] Graphically, FIB‐ing an image with every other pixel irradiated is the equivalent of half the ion dose, and the amplitude of a desired profile can be used to determine the filling ratio locally. Since the pixel size is much smaller than the SW wavelength, spin waves experience a smooth transition.…”