Calculation of magnetic exchange couplings in S=3/2 honeycomb system Bi${}_3$Mn${}_4$O${}_{12}$(NO${}_3$)} from first principles

Absence of magnetic ordering in Bi${}_3$Mn${}_4$O${}_{12}$(NO${}_3$), (BMNO) which has a magnetic subsystem that consists of honeycomb bi-layers of Mn${}^{4+}$ ions with spin S=3/2, has raised the expectation that its ground state is strongly frustrated due to longer-range antiferromagnetic interactions. We calculate the magnetic exchange coupling constants of the BMNO complex within a density functional approach and find that the dominating interactions between Mn spins are the antiferromagnetic nearest-neighbor $J_1$ and interlayer interaction $J_c$. The largest interaction is $J_c$, which substantially exceeds $J_1$. Longer-range interactions are antiferromagnetic, but only weakly frustrating.