Negligible spin-orbit coupling effect in the Mott-insulating antiferromagnet KRuO4

A comprehensive investigation of the electronic and magnetic properties of KRuO4 has been performed using the first-principles calculations in order to clarify the importance of Coulomb interaction and spin-orbit coupling effect. The results indicate that its ground state is of a G-type Mott-insulating antiferromagnet with nearest-neighbor antiferromagnetic coupling, and the computed magnetic moment of Ru7+ ion is 0.50 μB, in nice agreement with the observed value of 0.57(7) μB. In addition, the electronic structure near the Fermi level is dominated by strong hybridized Ru 4d and O 2p states. In sharply contrast with KOsO4, the significantly weaker spin orbit coupling of Ru 4d electrons has negligible impact on the electronic and magnetic properties of KRuO4, and the orbital contribution to the total moment is minor. On the other hand, the on-site Coulomb repulsion affects the band structure significantly, and is indispensable for appraising the electronic properties, opening the band gap, establishing the orbital ordering of the quarter-filled eg manifold.