Intrinsic room-temperature multiferroicity in a two-dimensional TiCr2O4 semiconductor with out-of-plane magnetic anisotropy and vertical piezoelectricity

Low-dimensional multiferroic compounds are promising candidate materials for advanced multistate information devices, while most known multiferroics do not show macroscopic magnetic and ferroelectric orders at room temperature, becoming a serious barrier for practical applications. Based on the first-principles density-functional theory, we propose a two-dimensional ${\mathrm{TiCr}}_{2}{\mathrm{O}}_{4}$ semiconductor with coexisting ferroelectricity and room-temperature ferromagnetism. The ${\mathrm{TiCr}}_{2}{\mathrm{O}}_{4}$ monolayer presents ferromagnetic coupling, out-of-plane magnetic anisotropy, spontaneous perpendicular polarization of up to $0.12\phantom{\rule{0.16em}{0ex}}\mathrm{C}/{\mathrm{m}}^{2}$, and desired vertical piezoelectricity. Remarkably, the conductivity can be improved with robust out-of-plane magnetic anisotropy and ferromagnetism above room temperature in carrier-doped ${\mathrm{TiCr}}_{2}{\mathrm{O}}_{4}$ monolayer. Our work shows that the ${\mathrm{TiCr}}_{2}{\mathrm{O}}_{4}$ monolayer is a promising candidate for low-dimensional nonvolatile spintronic field-effect transistors.