  Recent advancements in 2D magnetic materials have attracted a growing
interest driven by their unique properties and potential applications in
spintronic devices. However, the scarcity of systems that exhibit magnetism at
room-temperature has limited their practical implementation into functional
devices. In this work we focus on the recently synthetised van der Waals (vdW)
ferromagnet Fe$_3$GaTe$_2$, which exhibits above-room-temperature magnetism
(T$_{\mathrm{c}}$ = 350-380 K) and strong perpendicular magnetic anisotropy.
Through first-principles calculations, we examine the magnetic properties of
Fe$_3$GaTe$_2$ and compare them with the widely known Fe$_3$GeTe$_2$
ferromagnet. Our calculations unveil the complex microscopic mechanisms
governing their magnetic behaviour, emphasizing the pivotal role of the
ferromagnetic in-plane exchange interactions in the stabilization of the
elevated T$_{\mathrm{c}}$ in Fe$_3$GaTe$_2$. Additionally, we predict the
stability, strong perpendicular anisotropy and high T$_{\mathrm{c}}$ of
single-layer Fe$_3$GaTe$_2$. We also demonstrate the potential of strain
engineering and electrostatic doping to modulate its magnetic exchange
interactions and anisotropy. Our results incentivise the isolation of the
monolayer and pave the way for the future optimization of Fe$_3$GaTe$_2$ in
magnetic and spintronic nanodevices.
