  Fe$_{3-x}$GeTe$_2$ is a layered van der Waals magnetic material with a
relatively high ordering temperature and large anisotropy. While most studies
have concluded the interlayer ordering to be ferromagnetic, there have also
been reports of interlayer antiferromagnetism in Fe$_{3-x}$GeTe$_2$. Here, we
investigate the interlayer magnetic ordering by neutron diffraction
experiments, scanning tunneling microscopy (STM) and spin-polarized STM
measurements, density functional theory plus U calculations and STM
simulations. We conclude that the layers of Fe$_{3-x}$GeTe$_2$ are coupled
ferromagnetically and that in order to capture the magnetic and electronic
properties of Fe$_{3-x}$GeTe$_2$ within density functional theory, Hubbard U
corrections need to be taken into account.
