Interlayer magnetism in Fe3-xGeTe2

Fe3-xGeTe2 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 Fe3-xGeTe2. 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 Fe3-xGeTe2 are coupled ferromagnetically and that in order to capture the magnetic and electronic properties of Fe3-xGeTe2 within density functional theory, Hubbard U corrections need to be taken into account.