Triferroic Janus Semiconducting Bilayer with Tunable Intrinsic Multiferroic Coupling for Nonvolatile Memory

Recent reports on two-dimensional sliding ferroelectricity have demonstrated the huge potential of such materials in next-generation nonvolatile memory technologies. The coupling between two-dimensional sliding ferroelectricity, ferrovalley, and magnetism can simultaneously realize the electrical control of valley polarization, the electrical control of magnetic properties, and the magnetic control of valley polarization, which will further expand the practical applications of sliding ferroelectrics and provide opportunities for the development of spintronics and valleytronics. However, the extreme scarcity of such triferroic multiferroic materials discovered so far greatly limits related research. Here, we discovered a real semiconducting triferroic multiferroic material: a Janus 2H-VSeS bilayer. Based on first-principles calculations, in the back-to-back stacking configuration, the Janus 2H-VSeS bilayer exhibits the coexistence of sliding ferroelectricity, ferrovalley, and antiferromagnetic (AFM) characteristics and behaves as a semiconductor. We further found that ferrovalley can be controlled by ferroelectricity and antiferromagnetism through a band structure analysis. Numerical calculations show that the valley polarization has a linear correlation with the electric polarization, and a relatively small electric field can achieve a linear magnetoelectric coupling effect, all of which give rise to attractive intrinsic multiferroic coupling. Moreover, the vertical electric polarization and valley polarization nearly double when the interlayer distance is compressed by 10%, resulting in a rare piezo-multiferroic effect. We revealed that the ferroelectric polarization, valley polarization, and magnetic anisotropy energy of the Janus 2H-VSeS bilayer can be modulated by biaxial strains. Our findings indicate that the Janus VSeS bilayer holds broad prospects in high-performance nonvolatile memory, the development of new electronic devices, and multifunctional sensors.