Optimized Effective Potential Model for the Double Perovskites Sr2-xYxVMoO6 and Sr2-xYxVTcO6

TL;DR

This study develops an effective low-energy model for double perovskites Sr2-xYxVMoO6 and Sr2-xYxVTcO6, using first-principles calculations and the optimized effective potential method to analyze their magnetic and electronic properties.

Contribution

It introduces a rigorous parameter derivation and applies the optimized effective potential method to explore magnetic states, revealing complex magnetic ground states and methodological insights.

Findings

All ferromagnetic states are expected to be half-metallic.

Most ferrimagnetic states are metallic, with Y2VTcO6 being fully insulating.

Many ferrimagnetic structures are unstable against spin-spiral alignment.

Abstract

In attempt to explore half-metallic properties of the double perovskites Sr2-xYxVMoO6 and Sr2-xYxVTcO6, we construct an effective low-energy model, which describes the behavior of the t2g-states of these compounds. All parameters of such model are derived rigorously on the basis of first-principles electronic structure calculations. In order to solve this model we employ the optimized effective potential method and treat the correlation interactions in the random phase approximation. Although correlation interactions considerably reduce the intraatomic exchange splitting in comparison with the Hartree-Fock method, this splitting still substantially exceeds the typical values obtained in the local-spin-density approximation (LSDA), which alters many predictions based on the LSDA. Our main results are summarized as follows: (i) all ferromagnetic states are expected to be half-metallic. However, their energies are generally higher than those of the ferrimagnetic ordering between V- and Mo/Tc-sites (except Sr2VMoO6); (ii) all ferrimagnetic states are metallic (except fully insulating Y2VTcO6) and no half-metallic antiferromagnetism has been found; (iii) moreover, many of the ferrimagnetic structures appear to be unstable with respect to the spin-spiral alignment. Thus, the true magnetic ground state of the most of these systems is expected to be more complex. In addition, we discuss several methodological issues related to the nonuniqueness of the effective potential for the magnetic half-metallic and insulating states.