  Among several well-known transition metal-based compounds, the van der Waals
(vdW) Fe3-xGeTe2 (FGT) magnet is a strong candidate for use in two-dimensional
(2D) magnetic devices due to its strong perpendicular magnetic anisotropy,
sizeable Curie temperature (TC ~ 154 K), and versatile magnetic character that
is retained in the low-dimensional limit. While the TC remains far too low for
practical applications, there has been a successful push toward improving it
via external driving forces such as pressure, irradiation, and doping. Here we
present experimental evidence of a novel room-temperature (RT) ferromagnetic
phase induced by the electrochemical intercalation of common tetrabutylammonium
cations (TBA+) into FGT bulk crystals. We obtained Curie temperatures as high
as 350 K with chemical and physical stability of the intercalated compound. The
temperature-dependent Raman measurements in combination with vdW-corrected ab
initio calculations suggest that charge transfer (electron doping) upon
intercalation could lead to the observation of RT ferromagnetism. This work
demonstrates that molecular intercalation is a viable route in realizing
high-temperature vdW magnets in an inexpensive and reliable manner.
