Abstract

We present our recent experimental results on the observation and investigation of terahertz spin excitations (magnons) in various ferromagnetic layered structures. We discuss how one may tune the properties of the confined magnon modes and achieve entirely different in-plane magnon dispersions, characterized by positive and negative group velocities. Comparing the results to those calculated based on linear-response time-dependent density functional theory, we comment on the physical mechanism behind the decay of these magnonic states.

Next, we unravel the origin of different magnonic bands in layered ferromagnets and bring the topic of magnonic surface and interface states into discussion. We provide experimental examples of synthetic layered structures, supporting our discussions and show that the magnonic surface and interface states can be tailored in artificially fabricated layered structures. We demonstrate that the magnonic surface or interface states may show peculiar features. Moreover, we propose a method for quantum engineering of the magnonic band structure and demonstrate the possibility of designing an atomic scale magnonic crystal.

Finally, we briefly discuss the spin dependence of collective charge excitations at the surface of topological insulators (TIs). We discuss how such spin-dependent phenomena may be used to generate spin-polarized hot electrons at TIs surfaces.