Enhancement of Low‐k Spin‐Wave Transmission Efficiency with a Record‐High Group Velocity in YIG/Nonmagnetic Metal Heterojunctions

Abstract Improvement of transmission efficiency of spin waves in magnonic devices is crucial for high‐efficiency magnon‐based operations. However, existing techniques for enhancing spin‐wave detection signals, which either improve waveguide material quality or convert other forms of external energy into magnon energy, are still not efficient and convenient enough. Here, it is experimentally demonstrated that low‐k spin waves (where k is the wavenumber) transmission efficiency can be enhanced through yttrium iron garnet (YIG) surface metallization owing to the significantly increased group velocity and low spin‐pumping efficiency at low k. Given that the shielding effect of the conductive metal on YIG increases the spin‐wave group velocity from 55 to 132 km s⁻¹, the weak magnon‐dissipation mechanism of low‐k spin waves provides the foundation for signal enhancement. Through a detailed theoretical analysis on dispersion relations and spin‐wave amplitude, the detected signal strength is increased to 2 times for copper and 2.24 times for gold is verified. In detail the competition between the spin‐pumping effect is discussed and the enhanced group velocity is introduced by the metal decoration. This competition describes the essence of partial signal enhancement in the spin‐wave transmission spectrum. The work provides a practical way to achieve spin‐wave manipulation and low‐loss transmission.