Magnetic State Selected by Magnetic Dipole Interaction in Kagome Antiferromagnet NaBa${}_2$Mn${}_3$F${}_{11}$

Abstract

We have studied the ground state of the classical Kagome antiferromagnet NaBa${}_2$Mn${}_3$F${}_{11}$. Strong magnetic Bragg peaks observed in the $d$-spacing shorter than 6.0 Ã were indexed by the propagation vectors of ${\mathbf{k}}_0=(0,0,0)$. Additional peaks with weak intensities in the range of the $d$-spacing longer than 8.0 Ã were indexed by the incommensurate vectors of ${\mathbf{k}}_1=(0.3209(2),0.3209(2),0)$ and ${\mathbf{k}}_2=(0.3338(4),0.3338(4),0)$. Magnetic structure analysis exhibits that the 120${}^{\circ }$ structure with the {\it tail-chase} geometry having ${\mathbf{k}}_0$ is modulated by the incommensurate vectors. The classical calculation of the Kagome Heisenberg antiferromagnet having the antiferromagnetic 2nd-neighbor interaction, the ground state of which is degenerated 120${}^{\circ }$ structures with ${\mathbf{k}}_0$, reveals that the magnetic dipole-dipole (MDD) interaction including up to the 4th neighbor terms selects the tail-chase structure. The observed modulation of the tail-chase structure is indicated to be due to a small perturbation such as the long-range MDD interaction or the interlayer interaction.