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تسجيل مستخدم جديدMagnetic State Selected by Magnetic Dipole Interaction in Kagome Antiferromagnet NaBa$_{2}$Mn$_{3}$F$_{11}$
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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 AA were indexed by the propagation vectors of $boldsymbol{k}_{0} = (0,0,0)$. Additional peaks with weak intensities in the range of the $d$-spacing longer than 8.0 AA were indexed by the incommensurate vectors of $boldsymbol{k}_{1}=(0.3209(2),0.3209(2),0)$ and $boldsymbol{k}_{2}=(0.3338(4),0.3338(4),0)$. Magnetic structure analysis exhibits that the 120$^{circ}$ structure with the {it tail-chase} geometry having $boldsymbol{k}_0$ 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 $boldsymbol{k}_0$, 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.
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We performed inelastic neutron scattering measurements on a polycrystalline sample of a classical kagome antiferromagnet NaBa$_{2}$Mn$_{3}$F$_{11}$ to investigate the possibility of a dispersionless zero-energy excitation associated with rotation of
spins along the chains. The observed spectra indeed exhibit such an excitation with strong intensity at low energy, as well as dispersive excitations with weak intensity at high energy. Combining the measurements with calculations from linear spin-wave theory reveals that NaBa$_{2}$Mn$_{3}$F$_{11}$ is a good realization of the classical kagome antiferromagnet which exhibits a dispersionless mode lifted by the magnetic dipole-dipole interaction.
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