Magnetism and spin dynamics of above-room-temperature van der Waals ferromagnets using magnetization and ferromagnetic resonance measurements

Recent developments in two-dimensional (2D) magnetic materials have motivated the search for new van der Waals (vdWs) magnetic materials. Amongst such magnets, the materials with stable magnetic ordering at or above room temperature and metallic conductivity are most suitable for spintronic applications. Unfortunately, the majority of vdWs magnetic materials have low magnetic ordering temperatures much below room temperature or are highly insulating for electronic charge transport, making them largely unsuitable for spintronics. Recently, a vdW-type family of Fe-based compounds Fe_NGeTe₂ (N = 3, 4, and 5) have attracted intensive attention because of their near- or above-room-temperature itinerant ferromagnetism. In this work, we explored the magnetic properties of pristine and Ni-substituted Fe₅GeTe₂ single crystals grown with chemical vapor transport method. First, the magnetic properties of these compounds are characterized using temperature and field-dependent magnetization measurements. Then, the magnetization dynamics are probed using broadband ferromagnetic resonance (FMR) spectroscopy. The combination of low-temperature magnetization and cryo-FMR measurements provides a deeper understanding of magnetic anisotropy and exchange interactions in these compounds. Furthermore, our study also clarifies the effects of Ni substitution on the magnetic properties of Fe₅GeTe₂. This work offers a suitable platform to develop insights into low-dimensional magnetism and strategies to utilize it for potential applications in spintronics.