Optimized effective potential model for the double perovskitesSr2 − xYxVMoO6 andSr2 − xYxVTcO6

Abstract

In an attempt to explore half-metallic properties of the double perovskitesSr2 − xYxVMoO6 andSr2 − xYxVTcO6, we construct an effective low-energy model, which describes the behavior of thet2g states of these compounds. All parameters of such a model are derived rigorously on thebasis of first-principles electronic structure calculations. In order to solve this model,we employ the optimized effective potential method and treat the correlationinteractions in the random phase approximation. Although correlation interactionsconsiderably reduce the intraatomic exchange splitting in comparison with theHartree–Fock approach, this splitting still substantially exceeds the typical valuesobtained in the local-spin-density approximation (LSDA), which alters manypredictions based on the LSDA. Our main results are summarized as follows. (i) Allferromagnetic states are expected to be half-metallic. However, their energies are generallyhigher than those of the ferrimagnetic ordering between V and Mo/Tc sites (exceptSr2VMoO6). (ii) All ferrimagnetic states are metallic (except fully insulatingY2VTcO6) and no half-metallic antiferromagnetism has been found. (iii) Moreover, many of theferrimagnetic structures appear to be unstable with respect to the spin-spiral alignment.Thus, the true magnetic ground state of these systems is expected to be more complex.In addition, we discuss several methodological issues related to nonuniquenessof the effective potential for the half-metallic and magnetic insulating states.