Developing the half-metallic ferromagnetism in semimetal germanene monolayer: synergistic effects of band gap opening and magnetism engineering

Similar to graphene, the germanene monolayer could be a promising two-dimensional (2D) platform for spintronic applications. In this work, efficient doping routes are proposed to develop the half-metallic ferromagnetism in the germanene monolayer, based on the synergistic effects of band gap opening and magnetism engineering. The pristine germanene monolayer is a semimetal, exhibiting a Dirac cone originating mainly from the Ge-p_z state. The band gap opening can be achieved by doping with chalcogen atoms. Specifically, single S and Se impurities give a direct gap of 0.28 and 0.27 eV, respectively. This parameter increases up to 0.50 and 0.49 eV, respectively, when increasing the doping level. Moreover, Mn doping induces significant magnetism in the germanene monolayer with an overall magnetic moment of 3.78μ_B produced primarily by the Mn impurity. Herein, the antiferromagnetic semiconductor nature is obtained with a small energy gap of 0.05 eV. Further incorporating additional S and Se impurities causes a transition from the antiferromagnetic semiconductor state to a ferromagnetic half-metallic state, suggesting successful development of half-metallic ferromagnetism in the germanene monolayer. In these cases, the spin-down energy gap has values of 0.24 and 0.26 eV, respectively, while the spin-up state exhibits metallic character. Along with the state transition, codoping with chalcogen impurities also induces the switching from perpendicular magnetic anisotropy to in-plane magnetic anisotropy, which is of great importance for magnetic field sensing. In addition, our simulations confirm good thermodynamic stability of all the doped germanene systems. Our findings may introduce promising 2D spintronic materials with the desired half-metallic ferromagnetism, which can be prepared by codoping the germanene monolayer with chalcogen atoms and Mn transition metal.