Exchange Interactions in multi-correlated Spin-Orbit Systems

In condensed matter physics, we talk about spin-orbit-coupled solids when the spin-orbit coupling is comparable in energy with other relevant interactions. Spin-orbit coupling is a relativistic effect that couples the spin (magnetic) and orbital (charge) degrees of freedom. It substantially affects materials` structural, electronic, and magnetic properties. It can drastically change the physical interactions, leading to magnetic configurations never observed before. All these reasons have pushed the scientific interest toward materials where spin-orbit coupling has a strong impact. Among the recently discovered materials are notable examples of the 5d double perovskites. These are complex structures where the magnetic ions, belonging to the transition metal group of the periodic table, have a 5d electronic configuration. In these materials, exotic magnetic orderings that involve tilted magnetic structures or elusive ferromagnetic ordering of magnetic octupoles have been observed. Understanding how spin-orbit coupling activates or counteracts the other active interactions in forming the mentioned magnetic ground states poses significant challenges. However, first- principles calculations can provide a valuable solution by calculating the corresponding magnetic interactions "ab initio." The following project aims to study the interplay of spin-orbit coupling with structural effects and when magnetic ions have different valence on neighboring sites. The focus will be on pristine and chemically doped 5d1 double perovskites. We plan to extend an ab initio scheme for calculating magnetic interactions to multi-correlated structures (meaning with distinct characters of the magnetic ions) to accomplish the proposed goals. The research will be conducted in the host institution under Dr. Leonid Pourovskii at the Centre de Physique Thorique Ecole Polytechnique in Paris.