Two-Dimensional Half-Metallic and Semiconducting Lanthanide-Based MXenes

As a large family of two-dimensional materials, MXenes have attracted intensive attention in recent years. For more functional applications, it is of great significance to determine new MXene members. Here, we theoretically expand the M elements of MXenes to the lanthanide series. Based on density functional theory calculations, the bare lanthanide-based carbides M₂C (M = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) and the corresponding fluorine- and hydroxyl-terminated configurations are investigated. Most of the fluorine- and hydroxyl-terminated MXenes investigated are half-metals. Specifically, in the half-metallic Eu₂CF₂, the spin-down states show a band gap larger than 2 eV, implying this configuration's potential applications in spin generation and injection. Both Gd₂CT₂ (T = F and OH) are magnetic semiconductors. The former shows an indirect band gap of 1.38 eV, while the latter presents a direct one of 0.882 eV. These two configurations also show large magnetic moments higher than 13.7 μ_B per unit cell. All the hydroxyl-terminated MXene members show relatively low work functions, with the lowest value of 1.46 eV determined in Tm₂C(OH)₂. These predicted electronic properties imply that the lanthanide-based MXenes could have potential applications in spintronics, information storage, near-infrared detectors, field effect transistors, and field emitter cathodes.