  Van der Waals magnets have emerged as a fertile ground for the exploration of
highly tunable spin physics and spin-related technology. Two-dimensional (2D)
magnons in van der Waals magnets are collective excitation of spins under
strong confinement. Although considerable progress has been made in
understanding 2D magnons, a crucial magnon device called the van der Waals
magnon valve, in which the magnon signal can be completely and repeatedly
turned on and off electrically, has yet to be realized. Here we demonstrate
such magnon valves based on van der Waals antiferromagnetic insulator MnPS3. By
applying DC electric current through the gate electrode, we show that the
second harmonic thermal magnon (SHM) signal can be tuned from positive to
negative. The guaranteed zero crossing during this tuning demonstrates a
complete blocking of SHM transmission, arising from the nonlinear gate
dependence of the non-equilibrium magnon density in the 2D spin channel. Using
the switchable magnon valves we demonstrate a magnon-based inverter. These
results illustrate the potential of van der Waals anti-ferromagnets for
studying highly tunable spin-wave physics and for application in magnon-base
circuitry in future information technology.
