NMR investigation of anisotropic hyperfine coupling in van der Waals antiferromagnet FePS3

Anisotropic hyperfine coupling in the van der Waals antiferromagnet of iron phosphorous trisulfide FePS3 was probed through the 31P nuclear magnetic resonance (NMR) measurements. In this investigation, we aligned the crystalline specimen with the magnetic c* axis perpendicular and parallel to the external magnetic field. In the paramagnetic state, the temperature-dependent 31P NMR shift exhibits a distinct difference between these two alignments. Each transferred hyperfine coupling constant for the corresponding oriented direction was resolved. In the antiferromagnetic state, the single 31P NMR resonance line splits into a double-peak feature as the external field perpendicular to the c* axis while no such splitting behavior was discerned as the field applied along the c* axis. The observation indicates that the direction of the internal hyperfine field at the phosphorous site is parallel to the ab plane. In the vicinity of Neel temperature, the temperature evolution of the internal hyperfine field was found to obey a power law with a critical exponent of 0.125. Such a result provides microscopic evidence that the scenario of the Ising-type model is appropriate for the description of the magnetic interaction in FePS3.