  Intrinsic magnetic van der Waals (vdW) materials have attracted much
attention, especially Fe$_{3}$GeTe$_{2}$ (FGT), which exhibits highly tunable
properties. However, despite vast efforts, there are still several challenging
issues to be resolved. Here using a first-principles linear-response approach,
we carry out comprehensive investigation of both bulk and monolayer FGT. We
find that although the magnetic exchange interactions in FGT are frustrated,
our Monte Carlo simulations agree with the total energy calculations,
confirming that the ground state of bulk FGT is indeed ferromagnetic (FM). A
tiny electron doping reduces the magnetic frustration, resulting in significant
increasing of the Curie temperature. We also calculate the spin-wave
dispersion, and find a small spin gap as well as a nearly flat band in the
magnon spectra. These features can be used to compare with the future neutron
scattering measurement and finally clarify the microscopic magnetic mechanism
in this two-dimensional family materials.

Materials Science