  Dilute magnetic semiconductors, achieved through substitutional doping of
spin-polarized transition metals into semiconducting systems, enable
experimental modulation of spin dynamics in ways that hold great promise for
novel magneto-electric or magneto-optical devices, especially for
two-dimensional systems such as transition metal dichalcogenides that
accentuate interactions and activate valley degrees of freedom. Practical
applications of 2D magnetism will likely require room-temperature operation,
air stability, and (for magnetic semiconductors) the ability to achieve optimal
doping levels without dopant aggregation. Here we describe room-temperature
ferromagnetic order obtained in semiconducting vanadium-doped tungsten
disulfide monolayers produced by a reliable single-step film sulfidation method
across an exceptionally wide range of vanadium concentrations, up to 12 at%
with minimal dopant aggregation. These monolayers develop p-type transport as a
function of vanadium incorporation and rapidly reach ambipolarity.
Ferromagnetism peaks at an intermediate vanadium concentration of a few atomic
percent and decreases for higher concentrations, which is consistent with
quenching due to orbital hybridization at closer vanadium-vanadium spacings, as
supported by transmission electron microscopy, magnetometry and
first-principles calculations. Room-temperature two-dimensional dilute magnetic
semiconductors provide a new component to expand the functional scope of van
der Waals heterostructures and bring semiconducting magnetic 2D
heterostructures them into the realm of practical application.
