Analytical dispersion relation for forward volume spin waves in ferrimagnets near the angular momentum compensation condition

Antiferromagnetic magnonics has become the focus of intense scientific research because of the advantages of these materials compared to ferromagnets. However, ferrimagnetic materials have received much less attention despite exhibiting similar dynamical features at the angular momentum compensation point. In this paper, we present analytical expressions describing the dispersion relation of forward volume spin waves in ferrimagnetic materials near the angular momentum compensation point. We benchmark the derived dispersion relations against full micromagnetic simulations showing an excellent agreement between both approaches. We predict two different branches for forward volume spin waves in ferrimagnetic materials merging into a single branch at the angular momentum compensation point. Our results can assist in the design of magnonic devices built on ferrimagnetic materials.