Propagation Properties of Spin Wave in Non-Magnetic Metal-Covered YIG Waveguide

Spin-wave devices attract many interests because of their low Joule heating and power consumption. These devices can be categorized into a novel spintronic application and have been studied widely recently. A yttrium iron garnet (YIG) is widely used as a waveguide for these devices because of its low damping constant, meaning a long propagation length. To fabricate the waveguide, many groups etch the YIG to change it into a rectangular parallelepiped. However, the demagnetization field in the etched YIG is non-uniform, and spin-wave propagation properties are degraded. The different internal magnetic field in the YIG waveguide shows different dispersion curve. Hence the preferred wavelength of the spin wave is also different. To improve the propagation properties, we propose to use a metal-covered YIG waveguide in this paper. The wavelength of the spin wave propagating in a YIG waveguide covered by the non-magnetic metal film is two times longer than that in a non-coated YIG waveguide [1]. Thus, the spin wave can be reflected at the boundary between the meal-coated YIG and non-coated YIG area, providing waveguide functions.<br/>We prepared the YIG film epitaxially grown on gadolinium gallium garnet (GGG) substrate. The gold film was deposited onto the YIG film and formed into a waveguide shape using lithography. The &lt;0.5 T magnetic field was applied to this composite perpendicular to the film plane. The forward volume spin wave was excited and detected using a coplanar waveguide connected to a vector network analyzer (VNA). The wavelength of the propagated spin wave was about 9 micrometers, close to previous reports. The spin-wave spectroscopy was obtained, showing the Kittel curve, and splitting peaks because of the wavelength selectivity of the antennas.<br/>Furthermore, the width and length of the waveguide were varied, and spin-wave propagation properties were measured. These results indicated that the non-magnetic metal-covered YIG worked as a waveguide. We do not need to etch the YIG when we use this waveguide, increasing the uniformity of the internal magnetic field and magnetization in the YIG film and intensity of propagated spin wave compared with the previously etched YIG waveguide. Therefore, we demonstrated the usefulness of the non-magnetic metal-covered YIG waveguide.<br/>[1] T. Goto, K. Shimada, Y. Nakamura, H. Uchida, and M. Inoue, "One-dimensional magnonic crystal with Cu stripes for forward volume spin waves," Phys. Rev. Applied 11, 014033 (2019).