Tuning of electronic structure, magnetic phase, and transition temperature in two-dimensional Cr-based Janus MXenes

Abstract

Two-dimensional (2D) transition metal carbides and nitrides, called as MXenes, displaying astonishing properties are emerged as a new class of 2D layered materials. In this study, we have studied the structural, electronic, and magnetic properties of 2D bare ${M}_{2}\mathrm{C}$ and Janus Cr-based ${MM}^{\ensuremath{'}}\mathrm{C}$ metal carbides $(M\ensuremath{\ne}{M}^{\ensuremath{'}}=\mathrm{Cr}, \mathrm{Ti}, \mathrm{Sc}, \mathrm{V})$ based on density functional theory. We found that 2D Janus ${MM}^{\ensuremath{'}}\mathrm{C}$ MXenes are dynamically and thermally stable and show unique electronic and magnetic properties which are not seen in their individual bare cases. Our calculated electronic band structures indicate that the Janus ${MM}^{\ensuremath{'}}\mathrm{C}$ MXenes have Dirac-type band dispersion as seen in stanene with tiny band gaps. In addition, all considered bare ${M}_{2}\mathrm{C}$ MXenes show metallic property. However, Janus CrScC has dilute magnetic semiconducting property, CrVC shows half-metallicity, and CrTiC shows metallic property which can easily turn to half-metallicity by external effects. Our extensive density functional theory and Monte Carlo calculations indicate that Janus ${MM}^{\ensuremath{'}}\mathrm{C}$ MXenes also show different magnetic properties than their bare cases. While ${\mathrm{Cr}}_{2}\mathrm{C}$ and ${\mathrm{Sc}}_{2}\mathrm{C}$ have ferromagnetic spin orientations with ${T}_{C}=2000$ and 226 K Curie temperatures, respectively, CrScC shows ferrimagnetic character with antiferromagnetic N\'eel spin orientation and has ${T}_{N}=1120$ K magnetic phase transition temperature between ferrimagnetic and paramagnetic phases. Finally, external magnetic field effects on each crystal have also been elucidated in detail. The numerical outcomes reveal that Janus Cr-based ${MM}^{\ensuremath{'}}\mathrm{C}$ metal carbides have some unusual and interesting hysteresis characters. Our investigations presented here are not only interesting from a theoretical perspective, but also they show that Janus ${MM}^{\ensuremath{'}}\mathrm{C}$ MXenes are promising candidates for future spintronic applications, which should encourage their synthesis.