Na Os O₃: a high Neel temperature 5d oxide

Abstract

The origin of a high Neel temperature in a 5d oxide, Na Os O₃, has been analyzed within the mean-field limit of a multiband Hubbard model and compared with the analogous 4d oxide, Sr Tc O₃. Our analysis shows that there are a lot of similarities in both of these oxides on the dependence of the effective exchange interaction strength (J₀) on the electron-electron interaction strength (U). However, the relevant value of U in each system puts them in different portions of the parameter space. Although the Neel temperature for Na Os O₃ is less than that for Sr Tc O₃, our results suggest that there could be examples among other 5d oxides that have a higher Neel temperature. We have also examined the stability of the G-type antiferromagnetic state found in Na Os O₃ as a function of electron doping within GGA + U calculations and find a robust G-type antiferromagnetic metallic state stabilized. The most surprising aspect of the doped results is the rigid bandlike evolution of the electronic structure, which indicates that the magnetism in Na Os O₃ is not driven by Fermi surface nesting.