Magnetism and electronic structure of La2ZnIrO6and La2MgIrO6: CandidateJeff=12Mott insulators

Abstract

We study experimentally and theoretically the electronic and magnetic properties of two insulating double perovskites that show similar atomic and electronic structure but different magnetic properties. In magnetization measurements, La${}_{2}$ZnIrO${}_{6}$ displays weak ferromagnetic behavior below 7.5 K, whereas La${}_{2}$MgIrO${}_{6}$ shows antiferromagnetic behavior below ${T}_{N}$ $=$ 12 K. Electronic structure calculations find that the weak ferromagnetic behavior observed in La${}_{2}$ZnIrO${}_{6}$ is in fact due to canted antiferromagnetism. The calculations also predict canted antiferromagnetic behavior in La${}_{2}$MgIrO${}_{6}$, but intriguingly, this was not observed. Neutron diffraction measurements confirm the essentially antiferromagnetic behavior of both systems but lack the sensitivity to resolve the small (0.22${\ensuremath{\mu}}_{\mathrm{B}}$/Ir) ferromagnetic component in La${}_{2}$ZnIrO${}_{6}$. Overall, the results presented here indicate the crucial role of spin-orbit coupling (SOC) and the on-site Coulomb repulsion on the magnetic, transport, and thermodynamic properties of both compounds. The electronic structure calculations show that both compounds, like Sr${}_{2}$IrO${}_{4}$, are ${J}_{\mathrm{eff}}$ $=$ 1/2 Mott insulators. Our present findings suggest that La${}_{2}$ZnIrO${}_{6}$ and La${}_{2}$MgIrO${}_{6}$ provide a new playground to study the interplay between SOC and on-site Coulomb repulsion in a 5d transition-metal oxide.