  Magnetic frustrations in two-dimensional materials provide a rich playground
to engineer unconventional phenomena such as non-collinear magnetic order and
quantum spin-liquid behavior. However, despite intense efforts, a realization
of tunable frustrated magnetic order in two-dimensional materials remains an
open challenge. Here we propose Coulomb engineering as a versatile strategy to
tailor magnetic ground states in layered materials. Using the proximal quantum
spin-liquid candidate 1T-TaS$_2$ as an example, we show how long-range Coulomb
interactions renormalize the low energy nearly flat band structure, leading to
a Heisenberg model which decisively depends on the Coulomb interactions. Based
on this, we show that superexchange couplings in the material can be precisely
tailored by means of environmental dielectric screening, ultimately allowing to
externally drive the material towards the quantum spin-liquid regime. Our
results put forward Coulomb engineering as a powerful tool to manipulate
magnetic properties of van der Waals materials.
