This book presents a systematic experimental study of magnetic excitations in magnetic materials with nontrivial structures. It shows how unconventional magnetic order, topology, and microscopic interactions shape spin dynamics and highlights their significance for both fundamental physics and future spintronic functionalities. Spin–spin interactions sensitively reflect crystal structure and the underlying electronic states, allowing magnetic materials to host a rich variety of ordered spin states, including topological spin textures such as skyrmions. These textures have attracted broad interest due to their topology, emergent electromagnetic fields, and potential applications to magnetic and electrical devices. In addition, structurally unconventional magnets can exhibit multiple excitation modes, some of which can be selectively driven by external microwave magnetic fields. Such behavior has attracted considerable attention in spintronics due to its potential to future engineering applications. However, despite the rapid growth in reported magnetic materials, the dynamical properties of their magnetic excitations remains largely unexplored. To address this gap, this book investigates magnetic excitations in exotic magnets with unconventional structural features, combining material-specific experiments, microscopic modeling, and numerical simulations. Measurement platforms are designed to match the essential characteristics of the material, and the resulting data are analyzed using spin models that capture the key underlying interactions. This combined approach enables a detailed microscopic understanding of the observed excitations and offers one of the first systematic characterizations of magnetic dynamics in exotic magnets. The results provide a basis for both the fundamental understanding of nontrivial magnetic materials and their future development as functional platforms for spintronic applications.

Tomonao Araki is a postdoctoral researcher in experimental condensed matter physics at the RIKEN Center for Emergent Matter Science (CEMS), Japan. He received his Ph.D. in applied physics from The University of Tokyo in March 2026. His research focuses on the control and exploration of quantum magnonic phenomena in ultra-low-temperature environments. In particular, he investigates the manipulation and detection of magnon states in unconventional magnetic materials with nontrivial magnetic structures beyond simple ferromagnetism.