Insights into the complex magnetic orders of rare-earth nickelates
Rare-earth nickelate systems have received significant attention in recent years, due to their rich phase diagram containing a combined structural and metal-insulator transition, and additionally the formation of long-range magnetic order, which both can be tuned via the ionic size of rate-earth element. While the mechanism of the combined structural and metal-insulator transition is well studied, the nature of magnetic order is still under debate. Different experimental methods such as neutron diffraction and resonant X-ray scattering predict a complex magnetic order, which is predicted to be collinear or non-collinear, respectively. Within this talk I will present our recent theoretical results, which shed light on the nature of the complex magnetic ordering in rare-earth nickelate systems. Using density functional theory methods combined with Wannier function techniques, microscopic magnetic models were constructed, containing all relevant exchange interactions. Obtained models clearly explain the formation of experimentally observed antiferromagnetic order in the systems, while the inclusion of spin-orbit coupling effects demonstrates that the magnetic anisotropy is very small. Our results provide a clear picture of the trends of the magnetic order across the nickelate series, and give insights into the coupling between magnetic order and structural distortions.