Existence of multiple phases in double perovskite La₂CoTiO₆ under varying pressure

Double perovskites sparked a lot of attention in recent years due to their unique features including exotic magnetism, quantum spin-liquid, Mott insulating state, etc. The electronic states obtained from their d-orbitals determine the intriguing electrical and magnetic properties of transition metal oxides. External tuning parameter, such as hydrostatic pressure can drastically change physical properties. Here we study the first-principles density-functional theory spin-polarized electronic structure calculations for a rather simple, but with interesting physical properties, a double perovskite, namely, La₂CoTiO₆ where Ti is in 4⁺ state, i.e., nonmagnetic. The compound shows an antiferromagnetic ground state with T_N = 14.6 K [1]. At ambient pressure, the distorted structure (∠Co-O-Ti between 151–153°) shows an insulating behavior with a band gap of 0.999 eV consistent with the experiment. However, when the distortion is removed, namely, the undistorted structure (angle between Co-O-Ti is 180°) shows a very interesting ferromagnetic half-metallic (HM) behavior. With the application of hydrostatic pressure on the distorted structure, applied maximum 130 GPa, the system transforms to a metallic state (Mott transition) from an insulating state via a HM phase, which could be interesting to study the spin-controlled electronics or spintronics.

Reference

1. K. L. Holman, Q. Huang, T. Klimczuk, K. Trzebiatowski, J. W. G. Bos, E. Morosan, J. W. Lynn, and R. J. Cava, J. Solid State Chem. 180, 75 (2007).