Effects of biaxial strain on the impurity-induced magnetism in P-doped graphene and N-doped silicene: A first principles study

The effects of biaxial strain on the impurity-induced magnetism in P-doped graphene (P-graphene) and N-doped silicene (N-silicene) are studied by means of spin-polarized density functional calculations, using the supercell approach. The calculations were performed for three different supercell sizes $4\times 4$, $5\times 5$, and $6\times 6$, in order to simulate three different dopant concentrations 3.1, 2.0 and 1.4 %, respectively. For both systems, the calculated magnetic moment is 1.0 $\mu_B$ per impurity atom for the three studied concentrations. From the analysis of the electronic structure and the total energy as a function of the magnetization, we show that a Stoner-type model describing the electronic instability of the narrow impurity band accounts for the origin of $sp$-magnetism in P-graphene and N-silicene. Under biaxial strain the impurity band dispersion increases and the magnetic moment gradually decreases, with the consequent collapse of the magnetization at moderate strain values. Thus, we found that biaxial strain induces a magnetic quantum phase transition in P-graphene and N-silicene.