We have studied the frustrated system YBaCo4O7 generally described as an alternating stacking of Kagome and triangular layers of magnetic ions on a trigonal lattice, by single crystal neutron diffraction experiments above the Neel ordering transition. Experimental data reveals pronounced magnetic diffuse scattering, which is successfully modeled by direct Monte-Carlo simulations. Long-range magnetic correlations are found along the c-axis, due to the presence of corner-sharing bipyramids, creating quasi one-dimensional order at finite temperature. In contrast, in the Kagome layers ab-plane, the spin-spin correlation function -displaying a short-range 120 degrees configuration- decays rapidly as typically found in spin-liquids. YBaCo4O7 experimentally realizes a new class of two-dimensional frustrated systems where the strong out-of-plane coupling does not lift the in-plane degeneracy, but instead act as an external "field".
@article{arxiv.0904.3690,
title = {Magnetic correlations in YBaCo4O7 probed by single-crystal neutron scattering},
author = {P. Manuel and L. C. Chapon and P. G. Radaelli and H. Zheng and J. F. Mitchell},
journal= {arXiv preprint arXiv:0904.3690},
year = {2011}
}