2D Kagome Ordering in the 3D Frustrated Spinel Li2Mn2O4
muSR experiments on the geometrically frustrated spinel oxide, Li2Mn2O4, show the development of spin correlations over a range of length scales with decreasing temperature. Increased relaxation below 150 K is consistent with the onset of spin correlations. Below 50 K, spin order on a length scale, which is long range for the muSR probe, appears abruptly in temperature, consistent with prior neutron diffraction results. The oscillations in the zero field asymmetry are analyzed using a three frequency model. By locating the muon site this is shown to be consistent with the unexpected 2D q = root 3 x root 3 structure on the Kagome planes proposed originally from neutron data. Longitudinal field data demonstrate that some spin dynamics persist even at 2 K. Thus, a very complex magnetic ground state, featuring the co-existence of long length scale 2D ordering and significant spin dynamics, is proposed. This is unusual considering the 3D topology of the Mn3+ spins in this material.