Element-dependent unique properties of Janus Cr2I3X3 (X = F, Cl, Br) monolayer: Insight from first-principles calculations

Two-dimensional (2D) intrinsic ferromagnetic (FM) semiconductors are important to develop low-dimensional spintronic devices. The recent discovery of FM CrI3 monolayer provides ample opportunities for the spintronic applications of atomically thin magnets. Breaking the structural inversion symmetry of CrI3 would result in some extraordinary physical characteristics. Through first-principles calculations, here we systematically studied the structural, electronic, magnetic and mechanical properties of 2D Janus Cr2I3X3 (X = F, Cl, Br) monolayers, and compared them with those of the pure CrX3 monolayers. The results show that the properties of the Janus Cr2I3X3 (X = F, Cl, Br) monolayers are not within the range between CrI3 and CrX3, but go beyond this range. With the decrease of the atomic number of X elements, from Br to F, the properties of Cr2I3X3 increasingly deviate from that of CrI3 or CrX3. All the element-dependent properties of Cr2I3X3 are closely related with the charge redistribution and structural distortion, which is originated from the substitution of Iodine atoms with X atoms (atomic layer substitution) in the Janus structures. Our study enriches the diversity of Janus 2D materials, and provides the theoretical guidance for the application in spintronic devices.