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

Abstract

We investigate the low temperature magnetic properties of a $S=\frac{5}{2}$ Heisenberg kagomé 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 $T_{\mathrm{N}}=1.3$ K and a characteristic magnetization plateau is observed at 1/3 of the saturation magnetization below $T^{\ast }\sim 5$ 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 $T_1\sim k_{B}T/\hslash S$, which both point to the presence of a semiclassical nematic spin liquid state predicted for the Heisenberg kagomé antiferromagnetic model or to the persistence of the zero-energy modes of the kagome lattice under large magnetic fields.

6 pages, 5 figures