Re/Ir@Os-doping induced insulator-to-metal transition in Mott-insulator Ca2FeOsO6: octahedral distortion effects

Abstract

Regardless of several investigations to elucidate the ground state of the strongly correlated electron systems in doped Mott-insulators (MIs), the origin of the doping-induced insulator-to-metal transition (IMT) remains a crucial and debatable subject in solid-state physics. Herein, we explore the consequences of Re/Ir-doping at the Os-site (Re/Ir@Os), on the physical properties of the MI ferrimagnetic (FiM) Ca₂FeOsO₆ double perovskite oxides using density functional theory calculations. The doped structures’ solidity is analyzed by computing the defect formation energies in terms of the dopant-rich situation, which confirms their growth credibility at ambient conditions along with mechanical and dynamical stabilities. Various FiM spin-ordering is taken into account in the doped structures to analyze the magnetic ground state, which is FiM-I/FiM-II in the Re/Ir@Os-doped system. Remarkably, an IMT is predicted in the Re/Ir@Os-doped structures, which is due to the admixture of the partially occupied 5d orbitals of these ions. The calculated partial spin magnetic moments (m_s) of +4.12, −1.58, −0.75 and +0.88μ_B on the Fe, Os, Re, and Ir ions, endorse the +3, +5, +5, and +4 states having electronic configurations of t³_2g↑t⁰_2g↓e²_g↑e⁰_g↓, t³_2g↑t⁰_2g↓e⁰_g↑e⁰_g↓, t²_2g↑t⁰_2g↓e⁰_g↑e⁰_g↓, t³_2g↑t²_2g↓e⁰_g↑e⁰_g↓, respectively. The “+” and “−” signs on the ions m_s values, lead the systems into various FiM magnetic ordering. Moreover, the estimated Curie temperature (T_C) using the Heisenberg model in the pristine structure is 334 K, which is close to the experimentally observed value of 320 K along with a colossal uniaxial magneto crystalline anisotropy energy constant (K) of 2.95 × 10⁷ erg cm⁻³ having the easy magnetic axis of the ac-plane ([101]). It is established that T_C/K reduces and enhances to 298 K/1.33 × 10⁷ erg cm⁻³ and 365 K/4.71 × 10⁷ erg cm⁻³ for the Re@Os and Ir@Os-doped motif due to an increase and decrease in the octahedral distortions compared to that of the pristine system, respectively.