Tunable Magnetism and Transport Properties in Nitride MXenes Hemant Kumar, † Nathan C. Frey, † Liang Dong, † Babak Anasori, ‡ Yury Gogotsi, ‡ and Vivek B. Shenoy* ,† † Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States ‡ Department of Materials Science and Engineering and A.J. Drexel Nanomaterials Institute, Drexel University, Philadelphia, Pennsylvania 19104, United States * S Supporting Information ABSTRACT: Two-dimensional materials with intrinsic and robust ferromagnetism and half-metallicity are of great interest to explore the exciting physics and applications of nanoscale spintronic devices, but no such materials have been experimentally realized. In this study, we predict several M 2 NT x nitride MXene structures that display these characteristics based on a comprehensive study using a crystal field theory model and first-principles simulations. We demonstrate intrinsic ferromagnetism in Mn 2 NT x with different surface terminations (T = O, OH, and F), as well as in Ti 2 NO 2 and Cr 2 NO 2 . High magnetic moments (up to 9 μ B per unit cell), high Curie temperatures (1877 to 566 K), robust ferromagnetism, and intrinsic half-metallic transport behavior of these MXenes suggest that they are promising candidates for spintronic applications, which should stimulate interest in their synthesis. KEYWORDS: 2D materials, MXenes, half-metals, ferromagnetism, DFT, spintronics F ollowing the discovery of graphene, different types of two-dimensional (2D) materials such as transition-metal dichalcogenides (TMDs), silicene, and phosphorene have been synthesized. 1-3 These materials exhibit a wide range of physical properties that are being actively sought to fabricate high-performance electronic devices. While efforts in this area have been focused on the investigation of 2D semiconductors and optoelectronic materials, 2D magnetic materials remain largely unexplored. Robust and tunable magnetic properties in 2D materials can be valuable in quantum computation, logic and memory operations, spintronics, and other electronic devices where the spin degree of freedom of the carriers is manipulated. 4-7 Most of the 2D materials synthesized so far are intrinsically nonmagnetic. Several experimental approaches to induce magnetism in these materials, such as doping, quantum confinement, and surface functionalization, have been demon- strated recently. 8-10 For example, weak magnetism can be induced in graphene by doping it with nitrogen; zigzag edges of graphene nanoribbons exhibit half-metallic ferromagnetism in the presence of a strong electric field. 9,11 Similarly, edges/grain boundaries of TMDs have been shown to exhibit spin polarization. 12 However, such systems have very limited practical applications considering that inducing magnetism in a controllable manner in these materials systems remains a challenge, and the induced magnetism is usually not robust. 12 Fortunately, 2D transition-metal carbides, nitrides, and carbonitrides, known as MXenes, with a general formula of M n+1 X n T x (M = transition metals, X = C and/or N, T = O, OH, F, n =1-3), provide opportunities to achieve intrinsic 2D magnetism and half-metallicity as a few MXenes (such as Cr 2 C and Mn 2 C) have been predicted to be intrinsically magnetic. 13-17 Recent success in synthesizing ordered double-transition-metal (M 2 M′ n X n+1 T 2 , n = 1-2; e . g., Mo 2 TiC 2 T 2 ) MXenes adds to the diversity of the MXene family. 18 As a result, more than 20 types of MXenes with different transition metals and differing atomic layers (including Ti 2 CT x ,V 2 CT x , Nb 2 CT x , Ti 3 C 2 T x , Ti 4 N 3 T x , Mo 2 TiC 2 T x ) have already been synthesized, and approximately 70 different MXenes have been proposed theoretically, 19 not counting millions of solid solutions possible in various M-X systems. Among these, only one nitride MXene (Ti 4 N 3 T x ) has been reported. 20 Very recently, by using a salt-templated method and reduction of transition-metal oxides, 2D sheets of MoN, V 2 N, and W 2 N have been synthesized, which further adds to the family of possible 2D transition-metal carbides and nitrides. 21 Due to such diverse chemical compositions, a wide range of magnetic properties should be expected, and MXenes with any desired magnetic property can potentially be achieved with proper combinations of transition-metal elements and surface termination groups. Received: April 13, 2017 Accepted: May 30, 2017 Article www.acsnano.org © XXXX American Chemical Society A DOI: 10.1021/acsnano.7b02578 ACS Nano XXXX, XXX, XXX-XXX