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 ${MM}^{\prime }\mathrm{C}$ metal carbides $(M\ne M^{\prime }=\mathrm{Cr}, \mathrm{Ti}, \mathrm{Sc}, \mathrm{V})$ based on density functional theory. We found that 2D Janus ${MM}^{\prime }\mathrm{C}$ 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 ${MM}^{\prime }\mathrm{C}$ 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 ${MM}^{\prime }\mathrm{C}$ 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 Néel 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 ${MM}^{\prime }\mathrm{C}$ 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 ${MM}^{\prime }\mathrm{C}$ MXenes are promising candidates for future spintronic applications, which should encourage their synthesis.

中文翻译：

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二维铬基 Janus MXenes 电子结构、磁相和转变温度的调整

二维 (2D) 过渡金属碳化物和氮化物，称为 MXenes，显示出惊人的特性，作为一种新型的 2D 层状材料出现。在这项研究中，我们研究了二维裸片的结构、电子和磁特性。${米}_2\mathrm{C}$ 和 Janus Cr 为基础的 ${米米}^{\prime }\mathrm{C}$ 金属碳化物 $(米\ne {米}^{\prime }=铬, 钛, \mathrm{科学}, \mathrm{伏})$基于密度泛函理论。我们发现 2D Janus${米米}^{\prime }\mathrm{C}$MXenes 具有动态和热稳定性，并显示出独特的电子和磁性特性，这在其单独的裸机中是看不到的。我们计算出的电子能带结构表明 Janus${米米}^{\prime }\mathrm{C}$MXenes 具有 Dirac 型能带色散，如在具有微小带隙的 stanene 中所见。此外，都被认为是裸露的${米}_2\mathrm{C}$MXenes 显示出金属特性。然而，Janus CrScC 具有稀磁半导体特性，CrVC 显示出半金属性，而 CrTiC 显示出金属性，很容易受外部影响转变为半金属性。我们广泛的密度泛函理论和蒙特卡罗计算表明 Janus${米米}^{\prime }\mathrm{C}$MXenes 还显示出与其裸壳不同的磁性。尽管${铬}_2\mathrm{C}$ 和 ${\mathrm{科学}}_2\mathrm{C}$ 具有铁磁自旋方向 ${吨}_C=\mathrm{2000年}$ 分别在 226 K 居里温度和 226 K 居里温度下，CrScC 显示出具有反铁磁性 Néel 自旋取向的亚铁磁性特征，并具有 ${吨}_N=1120$ K 亚铁磁相和顺磁相之间的磁相变温度。最后，还详细阐明了外部磁场对每个晶体的影响。数值结果表明，基于 Janus Cr${米米}^{\prime }\mathrm{C}$金属碳化物具有一些不寻常且有趣的滞后特性。我们在此提出的调查不仅从理论角度来看很有趣，而且还表明 Janus${米米}^{\prime }\mathrm{C}$ MXenes 是未来自旋电子应用的有希望的候选者，这应该会鼓励它们的合成。