Roles of the band filling and the d orbitals hybridization on the conduction and magnetism of some Sr-based double perovskites: An LSDA+U study

We have systematically investigated the electronic structure and magnetic properties of the double perovskite oxides Sr₂CrZrO₆, Sr₂MnNbO₆, Sr₂FeMoO₆ and Sr₂NiRuO₆ in terms of band filling of different t_2g and e_g orbitals. Calculations of density of the states (DOS) were performed within the frame of the local spin density approximation and Hubbard potential (LSDA+U) employed in the Linear Muffin Tin Orbitals with Atomic Sphere Approximation (LMTO-ASA) method. The DOS of Sr₂FeMoO₆ was obtained and found to agree very well with published reports. Half-metallic character through the spin-down channel and the ferrimagnetic ordering was observed with notable hybridization among the 3d, p and 4d orbitals within Fermi level. A difference between the theoretically expected values and the calculated ones for the magnetic moment (Δm) of the 3d orbitals is determined and had been found to increase on going from Sr₂CrZrO₆ to Sr₂NiRuO₆. This increment in Δm indicates increment in the hybridization strength, which leads to long range ordering in Sr₂FeMoO₆ and Sr₂NiRuO₆ compounds. In comparison with reported experiments, the frustrated magnetism and weak ferrimagnetism states are the most possible ones in Sr₂CrZrO₆ in Sr₂MnNbO₆, respectively. The half-metallic character was also seen in Sr₂MnNbO₆ and Sr₂CrZrO₆ compounds while Sr₂NiRuO₆ shows normal metallic conduction and ferromagnetism in accordance with the superexchange interaction e_g²-o-e_g⁰ of Goodenough-Kanamori-Anderson (GKA).