Exploration of trivial and nontrivial electronic phases and of collinear and noncollinear magnetic phases in low-spin d5 perovskites

The 4d and 5d transition metal oxides have become important members of the emerging quantum materials family due to the competition between on-site Coulomb repulsion (U) and spin-orbit coupling (SOC). Specifically, the systems with d5 electronic configuration in an octahedral environment are found to be capable of possessing invariant semimetallic state and perturbations can lead to diverse magnetic phases. In this work, by formulating a multiband Hubbard model and performing SOC tunable density functional theory+U calculations on prototypes SrIrO3 and CaIrO3 and extending the analysis to other isostructural and isovalent compounds, we present eight quantum phases that can be observed in the family of low-spin d5 perovskites. In the cubic configuration, the U-SOC phase diagram shows stabilization of nonmagnetic metal phase in the weak U regime irrespective of the strength of SOC with the doubly degenerate t2g-J1/2 states occupying the Fermi surface. However, the system become ferromagnetic metal with increasing U while the SOC is maintained low. As the SOC increases, the moderate and higher values of U makes the transition to an antiferromagnetic metal and eventually to an antiferromagnetic insulating state. The GdFeO3-type orthorhombic distortion through tilting and rotation of the octahedra reform the t2g states through orbital intermixing to introduce a noncollinear spin arrangement. In the weak correlation regime, the nonmagnetic metal phase transform to ferromagnetic metal phase for weak SOC and an invariant Dirac semimetal phase for the strong SOC. On increasing the correlation strength, the ferromagnetic metal phase becomes insulating while the Dirac semimetal phase becomes a canted antiferromagnetic metal and finally transform to the canted antiferromagnetic insulating phase. Interestingly, in the higher U and higher SOC regimes the normal-spin (Sz) component vanishes to form a pure coplanar spin arrangement. The presence of several soft phase boundaries makes the family of d5 perovskites an ideal platform to study electronic and magnetic phase transitions under external stimuli.