Structural and Electronic Properties of the Magnetic and Nonmagnetic X_0.125Mg_0.875B₂ (X = Nb, Ni, Fe) Materials: A...

MgB₂ material has a simple composition and structure that is well-reported and characterized. This material has been widely studied and applied in the last 20 years as a superconductor in wire devices and storage material for H in the hydride form. MgB₂ doped with transition metals improves the superconductor behavior, such as the critical temperature (T _cs) or critical current (J _sc) for the superconducting state. The results obtained in this manuscript indicate that Nb-, Fe-, and Ni-doping in the Mg site leads to a contraction of the unit cell through the spin polarization on the electronic resonance of the boron layer. Fe and Ni transition metals doping perturb the electronic resonance because of stronger dopant-boron bonds. The unpaired electrons are transferred from 3d orbitals to the empty 2p orbitals of the boron atoms, locating α electrons in the σ bonds and β electrons in the π orbitals. The observed influence of magnetic dopants on MgB₂ enables the proposal of an electronic mechanism to explain the spin polarization of boron hexagonal rings.