Magnetic dynamics of two-dimensional itinerant ferromagnet Fe_3GeTe_2

Among the layered two-dimensional ferromagnetic materials (2D FMs), due to a relatively high T_C, the van der Waals (vdW) Fe₃GeTe₂ (FGT) crystal is of great importance for investigating its distinct magnetic properties. Here, we have carried out static and dynamic magnetization measurements of the FGT crystal with a Curie temperature T_C ≈ 204 K. The M-H hysteresis loops with in-plane and out-of-plane orientations show that FGT has a strong perpendicular magnetic anisotropy with the easy axis along its c-axis. Moreover, we have calculated the uniaxial magnetic anisotropy constant (K₁) from the SQUID measurements. The dynamic magnetic properties of FGT have been probed by utilizing the high sensitivity electron-spin-resonance (ESR) spectrometer at cryogenic temperatures. Based on an approximation of single magnetic domain mode, the K₁ and the effective damping constant (α_eff) have also been determined from the out-of-plane angular dependence of ferromagnetic resonance (FMR) spectra obtained at the temperature range of 185 K to T_C. We have found large magnetic damping with the effective damping constant α_eff～ 0.58 along with a broad linewidth (ΔH_pp> 1000 Oe at 9.48 GHz, H||c-axis). Our results provide useful dynamics information for the development of FGT-based spintronic devices.