Tunable valley polarization, magnetic anisotropy and dipole moment for layered Janus 2H–VSSe with intrinsic room temperature ferromagnetism

Highlights: • Electric field and strain effects on layered Janus 2H–VSSe are studied. • 2H–VSSe monolayer shows in-plane ferromagnetic ground states with Tc of 512 K. • Tunable valley splitting, magnetic anisotropy and dipole moment are observed. -- Abstract: Effects of strain, interlayer coupling and electric field on the valley polarization, magnetocrystalline anisotropy and dipole moment of layered Janus 2H–VSSe are systematically investigated by first-principles calculations. A unique V 3 d¹ electronic configuration and strong electron coupling interaction guarantee the stable in-plane ferromagnetic ground states with Tc of 512 K. By considering spin-orbit coupling (SOC) and exchange interaction based on the effective Hamiltonian k• p model, a large valley splitting of 94.8 meV is observed, which is mainly contributed by the spontaneous magnetic exchange field and not SOC effect. Under various bi-axis strains, Janus 2H–VSSe monolayer still maintains intrinsic in-plane ferromagnetism, but exhibits tunable valley polarization and magnetocrystalline anisotropy, which are associated with the in-plane d_x²_-y²/d_xy orbitals of V atoms. Importantly, stacking patterns can influence the spatial inversion symmetry and further alter the valley polarization for the layered Janus 2H–VSSe. Applied external electric-field can effectively control intrinsic built-in electric-field by charge redistribution in the vertical direction, which can remarkably change the dipole moments and slightly adjust the valley polarization. The layered Janus 2H–VSSe possesses intrinsic ferromagnetism, robust valley-contrasting physics and outfield-dependent dipole moment, making them competitive materials for practical applications in spin-valleytronics, optoelectronics and piezoelectric sensor.