Raman studies of the antiferromagnetic phase transition in atomically thin NiPS₃

NiPS₃ is one of the new class of layered magnetic materials, which can be exfoliated atomically thin films due to weak van der Waals bonding along the c-axis. It shows antiferromagnetic phase transition at the Néel temperature (T_N) of 155 K. For few-layer, as the dimension of the materials is changed from 3- to 2-dimension (2D), magnetic ordering can be affected. Raman spectroscopy is a powerful tool for studying 2D magnetic materials, as it can investigate phonon scattering as well as magnetic scattering. Below the T_N, the Raman spectrum of NiPS₃ shows anomalous features: 2-magnon scattering and a Breit-Wigner-Fano type signal. It also shows temperature dependent low-energy excitation due to spin fluctuations. Since these originate from the magnetic properties, the T_N of NiPS₃ can be estimated by using temperature dependence of these features. We prepared few-layer NiPS₃ samples by mechanically exfoliation. By conducting temperature dependent Raman measurement, we found the signatures of antiferromagnetic phase transitions in few-layer NiPS₃.