Structure, half-metallic and magnetic properties of bulk and (001) surface of Rb2XMoO6 (X = Cr, Sc) double perovskites: a DFT + U study

Abstract

Half-metallic (HM) ferromagnets (HM-FMs) with large HM gap and high Curie temperature (TC) have a great importance in the field of spintronics. In this study, the geometric features, electronic structure and magnetism of two new double perovskites (DPs) represented by Rb2XMoO6 (X = Cr, Sc) were explored in bulk phase and (001) surface using quantum mechanical total energy calculations based on density functional theory (DFT). The results showed that optimized lattice constant a is 7.96 Å and 8.26 Å for Rb2CrMoO6 (RCMO) and Rb2ScMoO6 (RSMO), respectively, in the cubic phase (space group Fm-3m, #225). The cohesive energy Ecoh, formation energy Efor and elastic constants (mechanical) calculations proved that present materials are stable. The magnetic properties were explored in terms of ground state magnetic coupling, total magnetic moment (M) and atomic magnetic moment (m), exchange energy (J), and Curie temperature. It was found that both materials have ferromagnetic coupling in the ground state, with M of integer value of 8.0 μ B (4.0 μ B), J value of 47 meV(72 meV) and TC of 365 K (557 K) in Rb2CrMoO6 (Rb2ScMoO6). The electronic properties computed with electronic band structure and density of states demonstrated both DPs to be half-metal with HM gap of 1.61 eV (2.1 eV) in Rb2Cr-based (Rb2Sc-based) system. Finally the electronic and magnetic properties of (001) surfaces were investigated and compared with that of bulk phase. Interestingly, bulk HM property was retained in RSMO, but disappeared in RCMO due the emergence of defect states at Fermi level (EF). The reported results suggest that Rb-based DPs carry some fascinating properties for spin-based devices.