Discrete surface magnons in low-loss epitaxial ferrimagnetic films

With the growing demand for faster and more energy-efficient data processing, conventional electronics face intrinsic limitations imposed by charge-based transport. Magnons—the quanta of spin waves—provide a promising alternative for low-energy and high-speed information transport, relying on magnetic materials with ultra-low damping. Recently, lithium aluminum ferrite (Li_0.5Al_1.0Fe_1.5O₄, LAFO), a ferrimagnetic insulator, has been found to exhibit ultra-low damping. Here, we investigate magnons in LAFO films of various thicknesses using Brillouin light scattering. Distinct magnon modes are observed, with up to three modes detected in 70-nm-thick films. From the magnetic-field dependence of the magnon frequencies, the exchange constant and magnetic anisotropy are extracted. In addition, broad frequency tunability and high group velocity are revealed. These results provide fundamental insights into thermally excited magnons in LAFO and establish a foundation for its application in next-generation magnonic devices.