Half-metal state of a Ti₂C monolayer by asymmetric surface decoration

Searching for two-dimensional (2D) ferromagnetic materials is one of the key steps in 2D spintronics. 2D metal carbide/nitride materials (MXene) are widely regarded as promising candidates for this kind of material. However, when the surfaces are saturated with some functional groups during the preparation, the ground states of most of the MXenes transit from ferromagnetic (FM) to antiferromagnetic (AFM) or non-magnetic (NM) states. In this article, we propose a new method to avoid this problem by adopting asymmetric decoration of the MXene surface, which can make MXenes ferromagnetic ground states. Based on hybrid density functional theory calculations, our results show asymmetrical adsorption of negative ions or metal atoms makes the Ti atoms have different valence states, such as one sublayer Ti4+ and another Ti+, which prefer FM ground states. This research will deepen our understanding of the magnetic properties of 2D materials and contribute to the design of new 2D ferromagnetic materials.