A Comparative DFT and DFT plus U Study on Magnetism in Nickel-Doped Wurtzite AlN

GGA and GGA+U formalisms have been implemented to comparatively study the electronic and magnetic properties of the Ni-doped AlN wurtzite semiconductor within density functional theory. Electronic structure calculations have been performed for ferromagnetic and antiferromagnetic states of Ni (x) Al1-x N (x = 0.056 and 0.0625) by GGA and GGA+U schemes. It has been found that the GGA+U method increases the repulsion of the impurity bands in the gap of semiconductors. The magnetic moment of the atom impurity in Ni (x) Al1-x N (x = 0.056 and 0.0625) is higher than those of the anions bonded to it for both GGA and GGA+U. Ni (N) contributions to the magnetic moment of Ni (x) Al1-x N (x = 0.056 and 0.0625) decrease (increase) in NiN4 tetrahedron when using GGA+U. A magnetic moment per Ni atom of about 2.10 mu B is predicted in Ni (x) Al1-x N for x = 0.056 with GGA approach for the most stable system. However, it was found that the ground state nature for Ni (x) Al1-x N (x = 0.056 and 0.625) changes from ferromagnetic to antiferromagnetic with the GGA+U approach for the Ni-Ni closest configuration. On the contrary, for the Ni-Ni farthest configuration both GGA and GGA+U formalisms predict a ferromagnetic ground state for Ni (x) Al1-x N (x = 0.056 and 0.0625). For intermediate Ni-Ni distances, both GGA and GGA+U schemes present almost the same energy differences and the same ferromagnetic ground state. The ferromagnetic ground state originates from the strong hybridization between Ni-d and N-p states. Additionally, it was found that the GGA+U formalism increases the magnetic moment per Ni atom for all Ni (x) Al1-x N (x = 0.056) ferromagnetic states.