From Non-Magnetic to Magnetic: A First-Principles Study of the Emergence of Magnetism in 2D (Nb_1-xTi_x)₄C₃ MXenes

MXene solid solutions have attracted intense attention due to their various properties that are potentially useful for emerging technological applications. In particular, magnetic 2D MXenes have been obtained typically using magnetic Cr, Mn, and V cations. Here, using first-principles calculations, we show that magnetic behavior comparable to that of the Cr-, Mn-, and V-containing MXenes can be obtained in a MXene solid solution (Nb_1-xTi_x)₄C₃ created from two non-magnetic end-members. The magnetization emerges due to the energetically driven segregation of Ti atoms on the solid solution surface that creates localized unpaired 3d electrons. The magnetic behavior of the solid solution is preserved upon the functionalization of the MXene surface by F and OH and is removed by functionalization with O. We show that variations in magnetism are primarily caused by differences in the locations of the titanium atoms. These findings suggest another approach for the design and tuning of magnetism in the 2D MXene family of materials.