Predictions of spin-valley properties in ferromagnetic Janus 2H-CeXY (X, Y = Cl, Br, I, X ≠ Y) monolayers: Merger of valleytronics with spintronics

In this work, the Janus 2H-CeXY monolayers are predicted as 2D intrinsic ferrovalley materials with bipolar ferromagnetic (FM) semiconductor characters, high T_c of 511–540 K, robust in-plane/perpendicular magnetic anisotropy (IMA/PMA) and spontaneous valley polarization through first-principles calculations. The d-p-d indirect exchange interaction between the Ce atom and X(Y) atoms is responsible for the observed FM ordering. Applying the biaxial strain ε from −6 % to 6 %, the Janus 2H-CeXY monolayers keep energy bandgap and large magnetic anisotropy. While a transition from PMA to IMA character is observed for the 2H-CeBrCl monolayer, which is due to the competition between Ce-p/d and Br/Cl-p orbitals. The intrinsic magnetic interaction and strong SOC effect induce a large spontaneous valley polarization of 29.1–78.7 meV for the Janus 2H-CeXY monolayers, which is also robust under various ε. Besides, the anomalous valley Hall effect (AVHE) can be observed due to the nonzero Ω_z(k) induced by the broken space/time-reversal symmetry. Overall, the Janus 2H-CeXY monolayers provides a new candidate for the spintronic and valleytronic devices.