The Ising triangular-lattice antiferromagnet neodymium heptatantalate as a quantum spin liquid candidate

Disordered magnetic states known as spin liquids are of paramount importance in both fundamental and applied science. A classical state of this kind was predicted for the Ising antiferromagnetic triangular model, while additional non-commuting exchange terms were proposed to induce its quantum version—a quantum spin liquid. However, these predictions have not yet been confirmed experimentally. Here, we report evidence for such a state in the triangular-lattice antiferromagnet NdTa 7 O 19 . We determine its magnetic ground state, which is characterized by effective spin-1/2 degrees of freedom with Ising-like nearest-neighbour correlations and gives rise to spin excitations persisting down to the lowest accessible temperature of 40 mK. Our study demonstrates the key role of strong spin–orbit coupling in stabilizing spin liquids that result from magnetic anisotropy and highlights the large family of rare-earth (RE) heptatantalates RETa 7 O 19 as a framework for realization of these states, which represent a promising platform for quantum applications. Neutron scattering, electron spin resonance, muon spectroscopy and magnetization measurements are applied to evidence a quantum spin liquid phase in NdTa 7 O 19 .