Yttrium-based Janus transition metal chalcogenides: Magnetic layered multiferroics*

The discovery of graphene in 2004 heralded the further discovery of hundreds of other two-dimensional (2D) materials, with a wide range of electronic and optical properties. Till recently, however, it was believed that magnetism cannot exist in 2D materials, in keeping with the Mermin-Wagner Theorem. This changed with the observation of long-ranged magnetism in a few 2D materials, such as CrI₃ and Cr₂Ge₂Te₆. This has started an active search for additional magnetic 2D crystals. In this talk, we present our theoretical research on a new class of magnetic 2D materials - Yttrium-based Janus transition metal chalcogenide (TMD) semiconductors. As a prototype of these materials, we studied properties of the YSSe Janus structure. YSSe has a magnetic moment of 1μ_B/formula unit (f.u.), and an in-plane magneto-crystalline anisotropy energy of 162 μeV/f.u. Along with broken time reversal symmetry, a YSSe layer also lacks mirror symmetry. Hence, it exhibits ferroelectricity, with a polarization that can be switched under the application of strain, making it a promising candidate material for ultra-compact spintronic and multiferroics-based devices.