An Electronic Correlation Approach to the Metal–Insulator Transition in the Half-Metallic Sr₂FeMoO₆Compound Doped With W

The ferromagnetic double perovskite Sr ₂ FeMoO ₆ (SFMO) system with half-metallicity and fairly high Curie temperature points to the possibility of designing spintronics materials operating at room temperature. On the other hand, the double perovskite Sr ₂ FeWO ₆ is an antiferromagnetic insulator with the W(5d) states located at high energies and also with completely different magnetic and electronic properties than the ferromagnetic SFMO. The ferromagnetism and half-metallicity in SFMO have been explained within a strongly correlated picture, in which Fe ³⁺ (3d ⁵ ) are localized spins in a high-spin S = 5/2 configuration and Mo ⁵⁺ (4d ¹ ) cores have one itinerant electron per formula unit (f.u.), which can hop to Fe sites only with an orientation antiparallel to that of the localized spin, thus stabilizing a ferromagnetic arrangement of local spins and fully opposite spin-polarized itinerant electrons. In this work, we study the effect of cationic doping on the behavior of \textT _C in SFMO with the Mo ions replaced by W ions, which leads to a metal-insulator transition. We use Green's function technique and the renormalization perturbation expansion method, in which the localized Fe spins and conduction Mo electrons interact via a double-exchange-type mechanism and the Hubbard model. Electronic correlations among the conduction electrons are included within a dynamical mean-field approach. Our results show a metal-insulator transition for W doping around x=0.2 in good agreement with experiments.