High-Speed and Long-Distance Spin-Wave Propagation in Spinel γ-Fe2O3 Epitaxial Thin Films

In spin wave (SW) devices, the modulation of SWs for computational units is necessary, imposing extremely high demands on material systems. In this study, high-quality epitaxial-grown spinel γ-Fe₂O₃ thin films on conductive Nb-doped SrTiO₃ substrates, achieving fast-speed, high-frequency, and long-distance SW propagation in this ferrimagnetic material, are developed. A novel two-step film growth technique using pulsed laser deposition is proposed and optimized, and the damping constant, exchange stiffness, and anisotropies of γ-Fe₂O₃ are determined. Compared to reported semiconductor magnetic materials, these epitaxial-grown γ-Fe₂O₃ thin films exhibit a significantly lower damping constant of 10⁻², representing a substantial advancement. Using finite-difference calculations, SW propagation is simulated, and vital information on transmission distance and dispersion curves is obtained. Experimental results show excellent agreement with these simulations. By applying a voltage to both sides of the conducting substrate, current across the film and SW device, resulting in the frequency shift of the SWs, is generated. These results demonstrate that high-quality γ-Fe₂O₃ films developed through the two-step growth method can efficiently propagate SWs, offering possibilities for various modulation methods in SW-based computing devices. This study positions spinel γ-Fe₂O₃ as a promising ferrimagnetic candidate for future applications in efficient SW modulation within computational systems.