We investigate the low temperature magnetic properties of a $S=\frac{5}{2}$ Heisenberg kagome antiferromagnet, the layered monodiphosphate ${\mathrm{Li}}_9{\mathrm{Fe}}_3({\mathrm{P}}_2{\mathrm{O}}_7{)}_3({\mathrm{PO}}_4{)}_2$, using magnetization measurements and ${}^{31}\mathrm{P}$ nuclear magnetic resonance. An antiferromagnetic-type order sets in at $T_N=1.3\mathrm{K}$ and a characteristic magnetization plateau is observed at $1/3$ of the saturation magnetization below $T^{*}\sim 5\mathrm{K}$. A moderate ${}^{31}\mathrm{P}$ NMR line broadening reveals the development of anisotropic short-range correlations concomitantly with a gapless spin-lattice relaxation time $T_1\sim k_{B}T/\hslash S$, which may point to the presence of a semiclassical nematic spin-liquid state predicted for the Heisenberg kagome antiferromagnetic model or to the persistence of the zero-energy modes of the kagome lattice under large magnetic fields.

• Received 4 February 2021
• Revised 14 July 2021
• Accepted 16 September 2021

DOI:https://doi.org/10.1103/PhysRevLett.127.157202