Classical Spin Liquid State in the $S=\frac{5}{2}$ Heisenberg Kagom\'e Antiferromagnet Li$_9$Fe$_3$(P$_2$O$_7$)$_3$(PO$_4$)$_2$

TL;DR

This study reveals a classical spin liquid state in a $S=5/2$ Heisenberg kagome antiferromagnet, characterized by short-range correlations and a magnetization plateau, suggesting the persistence of zero-energy modes or a nematic spin liquid phase.

Contribution

First experimental evidence of a classical spin liquid state in a high-spin Heisenberg kagome antiferromagnet using magnetization and NMR measurements.

Findings

Antiferromagnetic order at 1.3 K

Magnetization plateau at 1/3 saturation below 5 K

Gapless spin-lattice relaxation indicating a spin liquid state

Abstract

We investigate the low temperature magnetic properties of a $S=\frac{5}{2}$ Heisenberg kagom\'e antiferromagnet, the layered monodiphosphate Li$_9$Fe$_3$(P$_2$O$_7$)$_3$(PO$_4$)$_2$, using magnetization measurements and $^{31}$P nuclear magnetic resonance. An antiferromagnetic-type order sets in at $T_{\rm N}=1.3$ K and a characteristic magnetization plateau is observed at 1/3 of the saturation magnetization below $T^* \sim 5$ K. A moderate $^{31}$P NMR line broadening reveals the development of anisotropic short-range correlations within the plateau phase concomitantly with a gapless spin-lattice relaxation time $T_1 \sim k_B T / \hbar S$, which both point to the presence of a semiclassical nematic spin liquid state predicted for the Heisenberg kagom\'e antiferromagnetic model or to the persistence of the zero-energy modes of the kagome lattice under large magnetic fields.