Electron and Hole Doping Effects on the Magnetic Properties and Band Gap Energy of Ba2FeMoO6 and Sr2FeMoO6

Using the s-d model and Green's function theory, we investigated for the first time the electron and hole doping effects on the magnetic and optical properties of the double perovskites Ba2FeMoO6 (BFMO) and Sr2FeMoO6 (SFMO). Our aim was to find the doping ions that lead to an increase in Curie temperature TC. On the basis of a competition mechanism between spin exchange and s-d interactions, we explain at a microscopic level the decrease in magnetization <i>M</i> and band gap energy Eg, as well as the increase in TC of BFMO and SFMO through substitution with rare earth ions at the Ba(Sr) sites. The influence of doping with K at the Ba(Sr) and Co at the Fe sites on the magnetic properties and the band gap is also discussed. A very good qualitative coincidence with the existing experimental data was observed. Moreover, we found that both <i>M</i> and TC decrease with decreasing the size of BFMO and SFMO nanoparticles.