Din Babar Zaheer Ud, Fatheema Jameela, Arif Nimrah, Anwar M S, Gul Sundus, Iqbal Mudassir, Rizwan Syed
Physics Characterization and Simulations Lab (PCSL), Department of Physics, School of Natural Sciences (SNS), National University of Sciences and Technology (NUST) Islamabad 44000 Pakistan
Department of Chemistry, School of Natural Sciences (SNS), National University of Sciences and Technology (NUST) Islamabad 44000 Pakistan.
RSC Adv. 2020 Jul 7;10(43):25669-25678. doi: 10.1039/d0ra04568c. eCollection 2020 Jul 3.
Transition metal carbides (TMCs) have recently emerged as competent members among the family of two-dimensional (2D) materials, owing to their promising applications. There are many promising applications of MXenes; however, their magnetic properties lack a wide margin, both experimentally as well as theoretically, which needs to be investigated for potential use in spintronics. In this study, we carried out a comprehensive etching process selective extraction of Al layers from NbAlC-MAX using a wet electrochemical route under well-optimized conditions to obtain fine 2D-NbC MXene sheets. Structural analysis using X-ray diffraction (XRD) confirms the effective removal of Al followed by confirmation of a 2D layered structure from morphological analysis using scanning electron microscopy (SEM). Zero-field-cooled (ZFC) and field-cooled (FC) measurements of MAX and MXene at different field strengths were performed using a superconducting quantum interference device (SQUID). Magnetic measurements reveal the paramagnetic nature of NbAlC-MAX measured under 5 mT; however, this changes to a clear superconductor-like diamagnetic behavior with a shift of the magnetization from positive to negative values at low temperatures when measured under 5 mT and 10 mT for NbC MXene. The diamagnetism, however, is changed to paramagnetism at 100 mT, which shows the existence of critical fields known typically for a type-II superconductor. To gain an insight into this unusual behavior in MXene, density functional theory (DFT) first-principles calculation was also performed in Wein2K software using spin-polarized generalized gradient approximation (sp-GGA). The magnetic moment of the compound is calculated to be negative, which corresponds well with the experimental finding and suggests that the negative magnetic moment originated from the d-orbital of NbC. The present report provides a pathway to deeply understanding the existence of superconductivity-like diamagnetic behavior in NbC MXene, which is useful for future magnetic applications.
过渡金属碳化物（TMCs）因其具有广阔的应用前景，最近已成为二维（2D）材料家族中的重要成员。MXenes有许多有前景的应用；然而，它们的磁性在实验和理论上都存在很大差距，这需要进行研究以探索其在自旋电子学中的潜在用途。在本研究中，我们在优化条件下采用湿电化学路线，从NbAlC-MAX中进行了全面的蚀刻过程——选择性提取Al层，以获得精细的二维NbC MXene片材。使用X射线衍射（XRD）进行的结构分析证实了Al的有效去除，随后通过扫描电子显微镜（SEM）的形态分析确认了二维层状结构。使用超导量子干涉装置（SQUID）对MAX和MXene在不同场强下进行了零场冷却（ZFC）和场冷却（FC）测量。磁性测量揭示了在5 mT下测量的NbAlC-MAX的顺磁性质；然而，当在5 mT和10 mT下对NbC MXene进行低温测量时，这种性质转变为明显的类似超导体的抗磁行为，磁化强度从正值转变为负值。然而，在100 mT时抗磁性转变为顺磁性，这表明存在典型的II型超导体的临界场。为了深入了解MXene中的这种异常行为，还在Wein2K软件中使用自旋极化广义梯度近似（sp-GGA）进行了密度泛函理论（DFT）第一性原理计算。计算得出该化合物的磁矩为负，这与实验结果很好地对应，表明负磁矩源于NbC的d轨道。本报告为深入理解NbC MXene中类似超导的抗磁行为的存在提供了一条途径，这对未来的磁性应用很有用。
