(Invited) Ferromagnetism and Exchange Coupling with Fe-Doped WSe2

Abstract

The incorporation of magnetic dopants is a way to realize magnetism in semiconductors. The 2D material WSe2 is a semiconductor with a bandgap of 1.3 eV, and Fe-doped WSe2 is predicted to have room temperature, long-range ferromagnetism. Moreover, WSe2 has been extensively studied for applications in electronic devices, and can be prepared by deposition methods that are compatible with semiconductor fabrication processes. 2D magnetic films are particularly intriguing in technologies that rely on exchange coupling since the efficiency of the exchange with the magnet is inversely proportional to the magnet thickness 1/tFM. Chalcogenide-based TMD magnets can also have ideal interfaces with chalcogenide-based topological insulators (like Bi2Se3), enabling efficient spin torque devices and potentially realizing the quantum Hall effect without an external magnetic field.In this work, we demonstrate the growth of Fe-doped WSe2 and report on its up to room temperature ferromagnetic properties. The evolution of Fe-doped WSe2 films under different doping levels indicates that strain from the impurity atom itself coupled with strain imparted by the substrate can drive phase separation at high Fe concentrations. We find that suppressing that film strain helps promote more Fe incorporation (and higher Curie temperatures).Cr2O3 has only 0.2% lattice mismatch with WSe2 and is a magnetoelectric that can couple with ferromagnetic films. By using seed-layer techniques, we successfully prepared layered Fe-WSe2 on Cr2O3 and demonstrate magnetic coupling between the two, a potentially promising route toward realizing electric field control of 2D magnets. Magnetic measurements show a clear hysteresis loop at 100 K in a 2 Tesla cooling field, from which a large negative bias field of 600 Oe is resolved. The bias field vs temperature mesurements, where a negative bias field emerges below 250 K, indicates the existence of ferromagnetic exchange coupling in this heterostructure.This work is supported in part by NEWLIMITS, a center in nCORE, a Semiconductor Research Corporation (SRC) program sponsored by NIST through award number 70NANB17H041. This work is also supported by the National Science Foundation under awards 1917025 and 1921818.