^71 Ga NMR study on hexagonal La _3 FeGaS _7 with a chiral crystal structure

We report the results of ^71 Ga nuclear magnetic resonance (NMR) and magnetization measurements on a powder sample of hexagonal La _3 FeGaS _7 , which has a chiral crystal structure. The magnetization divided by the magnetic field, M(T)/H, shows a maximum around 180 K, suggesting the development of magnetic correlations within the one-dimensional chain of Fe atoms. A small anomaly in M(T)/H is also observed around 13 K. The ^71 Ga NMR spectrum above 80 K shows a typical powder pattern expected for nuclear spin I=3/2 , which is reproduced by simulations considering Zeeman and electric quadrupole interactions. The quadrupole frequency ν _Q obtained by the simulations is in good agreement with that obtained by our first-principles calculations. As the temperature is lowered, the ^71 Ga NMR signal intensity becomes weaker and disappears below 80 K. ^71 Ga NMR spectra with a broad line width and characteristic line shape are observed again below 23 K, indicating that La _3 FeGaS _7 undergoes long-range commensurate antiferromagnetic ordering. Upon further cooling, a distribution of the internal magnetic field at the Ga site is observed, suggesting the appearance of a disordered or incommensurate magnetic ordered state at 4 K.