2D Kagome Ordering in the 3D Frustrated Spinel Li2Mn2O4

TL;DR

This study uses muSR experiments to reveal complex magnetic ordering and persistent spin dynamics in the frustrated 3D spinel Li2Mn2O4, highlighting a coexistence of 2D order and ongoing spin fluctuations at low temperatures.

Contribution

It provides the first muSR evidence for 2D Kagome-like order and complex spin dynamics in Li2Mn2O4, connecting experimental observations with neutron diffraction data.

Findings

Detection of spin correlations developing below 150 K.

Observation of long-range 2D Kagome order below 50 K.

Persistent spin dynamics at 2 K indicating a complex magnetic ground state.

Abstract

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.