Fast long-wavelength exchange spin waves in partially-compensated Ga:YIG

TL;DR

This study demonstrates that Ga-substituted YIG films exhibit significantly higher exchange stiffness and faster spin-wave group velocities than pure YIG, enabling rapid, isotropic magnon transport in nano-scale devices.

Contribution

The paper provides direct measurement of enhanced exchange stiffness in Ga:YIG, showing its potential for high-speed magnonic applications in nano-structures.

Findings

Ga:YIG has three times larger exchange stiffness than pure YIG.

Spin-wave group velocity exceeds pure YIG for wavenumbers > 4 rad/μm.

Ga:YIG films have low damping and out-of-plane anisotropy.

Abstract

Spin waves in yttrium iron garnet (YIG) nano-structures attract increasing attention from the perspective of novel magnon-based data processing applications. For short wavelengths needed in small-scale devices, the group velocity is directly proportional to the spin-wave exchange stiffness constant $\lambda_\mathrm{ex}$. Using wave vector resolved Brillouin Light Scattering (BLS) spectroscopy, we directly measure $\lambda_\mathrm{ex}$ in Ga-substituted YIG thin films and show that it is about three times larger than for pure YIG. Consequently, the spin-wave group velocity overcomes the one in pure YIG for wavenumbers $k > 4$ rad/$\mu$m, and the ratio between the velocities reaches a constant value of around 3.4 for all $k > 20$ rad/$\mu$m. As revealed by vibrating-sample magnetometry (VSM) and ferromagnetic resonance (FMR) spectroscopy, Ga:YIG films with thicknesses down to 59 nm have a low Gilbert damping ($\alpha < 10^{-3}$), a decreased saturation magnetization $\mu_0 M_\mathrm{S}~\approx~20~$mT and a pronounced out-of-plane uniaxial anisotropy of about $\mu_0 H_{\textrm{u1}} \approx 95 $ mT which leads to an out-of-plane easy axis. Thus, Ga:YIG opens access to fast and isotropic spin-wave transport for all wavelengths in nano-scale systems independently of dipolar effects.