Emergence of strong room-temperature ferroelectricity and multiferroicity in 2D-Ti$_3$C$_2$T$_x$ free-standing MXene film

Abstract: Two-dimensional (2D) multiferroics are key candidate materials towards advancement of smart technology. Here, we employed a simple synthesis approach to address the long-awaited dream of developing ferroelectric and multiferroic 2D materials, specially in the new class of materials called MXenes. The etched Ti$_3$C$_2$T$_x$ MXene was first synthesized after HF-treatment followed by delamination process for successful synthesis of free-standing Ti$_3$C$_2$T$_x$ film. The free-standing film was then exposed to air at room-temperature as well as heated at different temperature to form TiO$_2$ layer derived from the Ti$_3$C$_2$T$_x$ MXene itself. TiO$_2$ is reported to be an incipient ferroelectric that assumes a ferroelectric phase in composite form. The structural and morphological analysis confirmed successful synthesis of free-standing film and the Raman spectroscopy revealed the formation of different phases of TiO$_2$. The ferroelectric measurement showed a clear polarization hysteresis loop at room-temperature. Also, the magnetic hysteresis was observed in the film indicating a possibility of coupling between ferroelectric and ferromagnetic phases at room-temperature. The magnetoelectric coupling test was also performed that showed a clear, switchable spontaneous polarization under applied magnetic field. This is the first report on existence of ferroelectric phase and multiferroic coupling in 2D free-standing MXene film at room-temperature which opens-up possibility of 2D materials-based electric and magnetic data storage applications at room-temperature.