Contents lists available at ScienceDirect Computational Materials Science journal homepage: www.elsevier.com/locate/commatsci Effects of electron-correlation, spin-orbit coupling, and modified Becke- Johnson potential in double perovskites SrLaBB′O 6 (B = Ni, Fe; B′ = Os, Ru) Dinesh Kumar Yadav a , Shalika Ram Bhandari a,b , Bishnu Prasad Belbase a , Gopi Chandra Kaphle a,b , Dibya Prakash Rai c , Madhav Prasad Ghimire a,b, ⁎ a Central Department of Physics, Tribhuvan University, Kirtipur-44613, Kathmandu, Nepal b Condensed Matter Physics Research Center, Butwal-11, Rupandehi, Nepal c Physical Sciences Research Center (PSRC), Pachhunga University College, Mizoram University, Aizawl 796001, India ARTICLE INFO Keywords: Double perovskites Spintronics Density functional theory Coulomb-interaction Spin orbit coupling Modified Becke-Johnson potential Mott-insulators ABSTRACT We investigate the electronic and magnetic properties of the newly synthesized SrLaBB′O 6 (B = Ni, Fe; B′ = Os, Ru) materials on the basis of density functional theory. Within local-density approximation (LDA), except for SrLaNiOsO 6 , the studied materials are found to be metallic. Inclusion of electron-correlation effects (U) and spin- orbit coupling (SOC) leads to the opening of the band gap at the Fermi level (E F ) for all the selected materials. Additionally modified Becke-Johnson (TB-mBJ) potential has been used which is found to enhance the band gap of 0.62 eV and 0.59 eV in SrLaNiOsO 6 and SrLaNiRuO 6 , respectively while remains metallic for the SrLaFeOsO 6 . The magnetic ground state is found to be antiferromagnetic (AFM) for SrLaNiOsO 6 and SrLaNiRuO 6 consistent with the experimental observations. Replacing Ni by Fe in SrLaNiOsO 6 resulted in SrLaFeOsO 6 . The ground state was found to be AFM. The co-operative effects of U and SOC opens a band gap ( ∼ 0.03 eV) dictating the sig- nificant influence on SrLaFeOsO 6 . On the otherhand, the Mott-insulating state is observed with a band gap opening of 0.33 eV and 0.58 eV for SrLaNiOsO 6 and SrLaNiRuO 6 , respectively with the dominant contributions from the Os-5d and Ru-4d bands at and around the Fermi level. The magnetic anisotropy suggests an easy axis along the [0 0 1]-direction. Charge ordering is found to be prominent in these compounds. Our result agrees well with the experimental findings. 1. Introduction The transition metal based double perovskites (DPs) are promising candidates due to the presence of d-orbitals which derives the fasci- nating chemical and physical properties. DPs exhibit diverse properties that includes metallicity, half-metallicity (HM), insulator, ferro- magnetism (FM), ferrimagnetism (FIM) and antiferromagnetism (AFM) [1,2], etc. As such, DPs are potential candidates for spintronics appli- cation that resulted in faster data transfer and huge memory storage devices. The other reason being their structural stability and variation in the crystal structures from simple cubic to highly distorted mono- clinic. The current research is mainly devoted to understand the structural, electronic and magnetic properties of such systems. There are two types of DP with chemical formula A 2 BB′O 6 and AA′BB′O 6 re- spectively, where A, A′ are alkaline earth or rare earth elements and B, B′ are the transition elements. Among the family of DPs, the compound with Osmium-oxides are found to be rarely investigated due to the safety measures and difficulties in laboratory fabrication, as osmium and oxygen are highly volatile, as reported in OsO 4 [3]. However, the successful synthesis of osmium-oxide based DPs such as SrLaNiOsO 6 and SrLaNiRuO 6 from solid state reactions technique [4] motivates us to carry out thorough investigation and analyse their novel physical properties by means of first principles density functional theory (DFT) approach. It is interesting to note that the novel properties can be achieved by structural modification of A, A′ and B, B′ sites. For example, observation of a magnetic insulating state in Sr 2 MOsO 6 (where M = Cu, Ni) [5], half semi-metallic AFM in Sr 2 CrTO 6 (T = Os, Ru) [6], etc. AFM Mott-insulating state with an indirect band gap of 0.25 eV and 0.15 eV in Ca 2 MgOsO 6 and Sr 2 MgOsO 6 , respectively under the effect of elec- tron-correlations [7], and opening of the charge gap of ∼ 0.17 eV in FM- Ba 2 NiOsO 6 was found under the co-operative effect of electron-corre- lation and spin-orbit coupling (SOC) plays significant role. Further- more, Ba 2 NiOsO 6 shows metamagnetic transition and Dirac-Mott in- sulating FM state near 100 K [8]. An unusual superconducting behaviour has been observed in AOs 2 O 7 (A = Cs, Rb and K) [9], mag- netically driven metal-insulator transition (MIT) in NaOsO 3 at Neel https://doi.org/10.1016/j.commatsci.2019.109168 Received 14 April 2019; Received in revised form 25 July 2019; Accepted 26 July 2019 ⁎ Corresponding author at: Central Department of Physics, Tribhuvan University, Kirtipur-44613, Kathmandu, Nepal. E-mail address: mpghimire@tucdp.edu.np (M.P. Ghimire). Computational Materials Science 170 (2019) 109168 0927-0256/ © 2019 Elsevier B.V. All rights reserved. T