German-Ukrainian Seminar on Quantum Materials

Lecture #9: April 20, 2023 at 14:00 Kyiv time (13:00 Dresden time)

Meeting ID: 992 8170 3595 // Passcode: 963908

Speaker: Alexander Yaresko, Max Planck Institute for Solid State Research, Stuttgart

Title: How much anisotropy is enough? LDA+U study of anisotropic magnetic interactions in Iridium oxide

Because of strong spin-orbit coupling of Iridium 5d electrons magnetic interaction in many Ir4+ oxides cannot be described by an isotropic Heisenberg-like model and anisotropic exchange interactions become important. In this work LSDA+U band structure calculations with constrained magnetization direction are used to study magnetic properties of some Ir oxides with edge- and corner-sharing IrO octahedra. Effective magnetic interactions are estimated by mapping calculated total energy differences onto appropriate effective models which include isotropic Heisenberg as well as bond-dependent anisotropic interactions. In Na2IrO3, with edge sharing IrO octahedra forming a honeycomb lattice, magnetic interactions are dominated by the symmetric anisotropic Kitaev term. In R2Ir2O7 iridates, with a pyrochlore crystal structure, nearest neighbor Ir-Ir bonds do not have inversion symmetry and antisymmetric Dzyaloshinskii-Moriya (DM) interaction is allowed. It stabilizes noncollinear all-in-all-out magnetic order in pyrochlore iridates with a small radius of a rear-earth ion R.