Effect of La3+/Sr2+ ordering on the magnetic properties of La2/3Sr1/3MnO3 by first principles calculations

In this work, using DFT + U formalism, we investigate the effect of order-disorder in the A-site occupation by La3+ and Sr2+ on the stability of the ferromagnetic order in La2/3Sr1/3MnO3 with R (3) over barc symmetry. To date, a detailed theoretical discussion of such phenomenon, using a combination of different representations of the electronic structure, is still missing in the Literature. We employed structural models consisting of 120 atom supercells constructed according to the precise stoichiometry of the compound. Two configurations, describing randomized and ordered occupation of the La3+/Sr2+ ions, were evaluated. We demonstrate that the ferromagnetic arrangement of La2/3Sr1/3MnO3 with randomly distributed La3+ and Sr2+ ions is more stable. In such configuration we find that the Mn3+ and Mn4+ ions are not distinguished, favoring the double-exchange mechanism, enhanced by the higher degree of covalence in the Mn-O bonds near the Fermi level between the spin-up Mn-e(g) orbitals and the O-p orbitals.