Remarkably enhanced ferromagnetism in a super-exchange governed Cr2Ge2Te6 monolayer via molecular adsorption

Manipulation of the electronic properties of 2D materials with molecular adsorption has been widely reported in the past decade. However, the impact of adsorption of molecules on the magnetism of intrinsic 2D magnets is not yet sufficiently understood. Inspired by the recent discovery of intrinsic 2D ferromagnetism in atomically thin Cr2Ge2Te6 and CrI3 crystals, in this investigation, the adsorption of gas molecules including CO, CO2, H2O, N-2, NH3, NO, NO2, O-2 and SO2 on the basal plane of a Cr2Ge2Te6 (CGT) monolayer was systematically investigated by density functional theory. The structures, energy, charge transfer, work function, and electronic and magnetic properties of the gas molecule adsorbed Cr2Ge2Te6 monolayers were explored. It has been found that the adsorption of gas molecules significantly influences the electronic and magnetic properties of a CGT sheet. It was observed that the adsorption of molecules could effectively enhance the ferromagnetism and Curie temperature (T-C) of the CGT sheet. Notably, a remarkable enhancement of ferromagnetism and T-C by 38% and 32% was achieved by the adsorption of NO and NO2, respectively. Moreover, NO2 adsorbed CGT exhibits a semiconductor-to-metal transition. The enhanced ferromagnetism and tunable electronic structure could be ascribed to the considerable charge transfer as well as to the alignment of the frontier molecular orbital. The outcome of this study reveals not only exciting insights into the environmental effect on 2D magnets but also provides a new candidate as a NO2 gas sensor.