  The outstanding optoelectronic and valleytronic properties of transition
metal dichalcogenides (TMDs) have triggered intense research efforts by the
scientific community. An alternative to induce long-range ferromagnetism (FM)
in TMDs is by introducing magnetic dopants to form a dilute magnetic
semiconductor. Enhancing ferromagnetism in these semiconductors not only
represents a key step towards modern TMD-based spintronics, but also enables
exploration of new and exciting dimensionality-driven magnetic phenomena. To
this end, we show tunable ferromagnetism at room temperature and a thermally
induced spin flip (TISF) in monolayers of V-doped WSe2. As vanadium
concentrations increase within the WSe2 monolayers the saturation magnetization
increases, and it is optimal at ~4at.% vanadium; the highest doping/alloying
level ever achieved for V-doped WSe2 monolayers. The TISF occurs at ~175 K and
becomes more pronounced upon increasing the temperature towards room
temperature. We demonstrate that TISF can be manipulated by changing the
vanadium concentration within the WSe2 monolayers. We attribute TISF to the
magnetic field and temperature dependent flipping of the nearest W-site
magnetic moments that are antiferromagnetically coupled to the V magnetic
moments in the ground state. This is fully supported by a recent spin-polarized
density functional theory calculation. Our findings pave the way for the
development of novel spintronic and valleytronic nanodevices based on
atomically thin magnetic semiconductors and stimulate further studies in this
rapidly expanding research field of 2D magnetism.
