  Li2MnO3 with a S=3/2 two-dimensional Mn honeycomb lattice has a Neel-type
antiferromagnetic transition at TN=36 K with a broad maximum in the magnetic
susceptibility at TM=48 K. We have investigated site percolation effects by
replacing Mn with nonmagnetic Ti, and completed a full phase diagram of
Li2Mn1-xTixO3 solid solution systems to find that the antiferromagnetic
transition is suppressed continuously without a clear sign of changes in the
Neel-type antiferromagnetic structure. The magnetic ordering eventually
disappears at a critical concentration of xc=0.7. This experimental observation
is consistent with percolation theories for a honeycomb lattice when one
considers up to 3rd nearest-neighbor interactions. This study highlights the
importance of interaction beyond nearest neighbors even for Mn element with
relative localized 3d electrons in the honeycomb lattice.
