The Role of Oxygen Vacancies in the Magnetic and Electronic Structure of La_0.7Sr_0.3MnO₃

Perovskite manganites host a variety of phenomena such as (anti)ferromagnetism, charge and orbital order, metal-insulator transitions, and colossal magnetoresistance that are highly sensitive to charge carrier density and crystal structure. As with cation substitution, oxygen vacancies can provide control over these parameters through electronic doping and steric effects. In our investigation, we consider the role of oxygen vacancies on the magnetic, electronic, and structural properties of La_0.7Sr_0.3MnO_3-δ within the DFT+U formalism. In order to isolate the effects of the vacancies, we utilize the Virtual Crystal Approximation to treat the La/Sr content. We report the cases when δ = 0.125, 0.25, and 0.5. For each system, we consider all symmetry inequivalent vacancy sites. We optimize each structure to determine the energetically favorable vacancy sites and magnetic ordering. For the low energy structures, we determine the vacancy formation energy, electronic structure, magnetic structure, magnetic exchange coupling parameters, and conductivity. From the results, we correlate the calculated properties with the effects of the vacancies on the orbital character.