Enhancement of ferromagnetism in δ-(Zn,Mn,Li)Se by shape deformation: Based on Zener's double exchange

Based on Zener's double exchange mechanism, hole concentration was increased to make the Fermi level just cross the middle of the impurity states in the gap. Meanwhile, shape deformation of the impurity states could also enhance the exchange energy of diluted magnetic semiconductor (DMS). In terms of the density functional calculations, mechanism of enhancement of exchange energy of δ-(Zn,Mn,Li)Se with shape deformation was investigated. Lattice parameter variation in the z-direction which was perpendicular to the Mn layer exerted a significant effect on the exchange energy, while it was not obvious in the x- or y-directions. Compared with pure ZnSe and δ-(Zn,Mn,Li)Se, p-type co-doping of Li had a significant effect on the atomic structure. Exchange energy could be enhanced mainly due to the higher antiferromagnetic peak on the Fermi surface with shape deformation. Such enhancement was useful to ferromagnetic double exchange, while harmful to antiferromagnetic super exchange. These results shed new light on the design of dilute magnetic semiconductors with shape deformation and p-type co-doping for spintronic applications.