Insulator-to-metal transition, magnetic anisotropy, and improved TC in a ferrimagnetic La2CoIrO6: strain influence

Abstract

The elegant interactions between Coulomb repulsion and spin–orbit coupling in Ir-based double perovskite oxides (DPO) normally induce peculiar magnetic behavior. Herein, we investigate the effect of the development of biaxial [110] strain on the formation energetics, and electronic and magnetic properties of the La₂CoIrO₆ DPO employing density functional theory calculations. Our results reveal that the unstrained motif is a Mott-insulator achieving an energy band gap of 0.35 eV with a ferrimagnetic (FiM) ground state, which essentially arises due to anti-ferromagnetic (AFM) coupling between the half-occupied Co t_2g and partially occupied Ir t_2g/empty e_g orbitals via oxygen 2p states. Along with this, it is found that [001] (c-axis) is the easy magnetic axis, which results in 12.5 meV total energy per u.c., obtaining a large anisotropy constant of 0.8 × 10⁸ erg cm⁻³. The computed partial spin-magnetic moments on the Co/Ir ion are 2.64/−0.46 μ_B, where the negative sign on the Ir ion moment confirms the AFM interactions between them. Additionally, the t_2g/e_g and t_2g orbital characteristics of Co²⁺ and Ir⁴⁺ ions are visible in the spin-magnetization density isosurfaces plot, respectively. Likewise, the estimated Curie temperature (T_C) using the Heisenberg model is 104 K, which is in agreement with the experimentally observed value of 94/97 K. Interestingly, an insulator-to-metal transition is achieved at a critical compressive strain of −6% with a robust FiM state, where the Co 3d_xy and Ir 5d_x²−y² orbitals are mainly responsible for metallicity. Simultaneously, the magnetocrystalline anisotropy energy and T_C can be sufficiently enhanced by applying compressive strain due to enhancement in the structural distortions. So this work suggested that the strain strategy is an efficient approach to tuning the properties of the compounds for their feasible realization in spintronics.