Two-dimensional5dmultiferroicW3Cl8: Breathing kagome lattice and tunable magneto-optical Kerr effect

Owing to the strong spin-orbit coupling and the related fascinating physical properties, heavy $5d$ transition metals exhibit desirable application prospects. However, up to now, the $5d$ magnetic materials are still very limited, especially very rare for tungsten. In this work, we theoretically predict a two-dimensional multiferroic ${\mathrm{W}}_3{\mathrm{Cl}}_8$ monolayer. Intrinsic $5d$ magnetism of tungsten is activated by the W ions’ fractional valence in a breathing kagome lattice of reduced effective dimension. A coplanar $Y$-type antiferromagnetism composed by ferromagnetic ${\mathrm{W}}_3$ trimers is confirmed as the magnetic ground state. The spontaneous ferroelectric polarization mainly originates from the ion displacement induced by the breathing distortion of kagome lattice. An intrinsic magneto-optical Kerr effect with sizable Kerr angle can be observed to detect this trimeric $Y$-type antiferromagnetism, and it depends strongly on the detailed magnetic order. Thereby, we propose a general scheme for realizing more $5d$ magnetism in two-dimensional multiferroic systems.