Manipulation of electronic and magnetic properties of M₂C (M=Hf, Nb, Sc, Ta, Ti, V, Zr) monolayer by applying mechanical strains

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Tuning the electronic and magnetic properties of a material through strain engineering is an effective strategy to enhance the performance of electronic and spintronic devices. Recently synthesized two-dimensional transition metal carbides M₂C (M=Hf, Nb, Sc, Ta, Ti, V, Zr), known as MXenes, has aroused increasingly attentions in nanoelectronic technology due to their unusual properties. In this paper, first-principles calculations based on density functional theory are carried out to investigate the electronic and magnetic properties of M₂C subjected to biaxial symmetric mechanical strains. At the strain-free state, all these MXenes exhibit no spontaneous magnetism except for Ti₂C and Zr₂C which show a magnetic moment of 1.92 and 1.25 μB/unit, respectively. As the tensile strain increases, the magnetic moments of MXenes are greatly enhanced and a transition from nonmagnetism to ferromagnetism is observed for those nonmagnetic MXenes at zero strains. The most distinct transition is found in Hf₂C, in which the magnetic moment is elevated to 1.5 μB/unit at a strain of 15%. We further show that the magnetic properties of Hf₂C are attributed to the band shift mainly composed of Hf(5d) states. This strain-tunable magnetism can be utilized to design future spintronics based on MXenes.