Robustness of ferromagnetism in van der Waals magnet Fe$_3$GeTe$_2$ to hydrostatic pressure

Two-dimensional van der Waals ferromagnet Fe$_3$GeTe$_2$ (FGT) holds a great potential for applications in spintronic devices, due to its high Curie temperature, easy tunability, and excellent structural stability in air. Theoretical studies have shown that pressure, as an external parameter, significantly affects its ferromagnetic properties. In this study, we have performed comprehensive high-pressure neutron powder diffraction (NPD) experiments on FGT up to 5 GPa, to investigate the evolution of its structural and magnetic properties with hydrostatic pressure. The NPD data clearly reveal the robustness of the ferromagnetism in FGT, despite of an apparent suppression by hydrostatic pressure. As the pressure increases from 0 to 5 GPa, the Curie temperature is found to decrease monotonically from 225(5) K to 175(5) K, together with a dramatically suppressed ordered moment of Fe, which is well supported by the first-principles calculations. Although no pressure-driven structural phase transition is observed up to 5 GPa, quantitative analysis on the changes of bond lengths and bond angles indicate a significant modification of the exchange interactions, which accounts for the pressure-induced suppression of the ferromagnetism in FGT.