Raman studies of van der Waals antiferromagnet NiPS₃

Two-dimensional (2D) van der Waals magnetic materials are attracting much interest both for the fundamental understanding of the physics in low dimensions and for possible applications in future spintronic devices. Due to the small volume of atomic-thickness specimens of such materials, optical spectroscopy has been extensively utilize in the study of 2D magnetic materials. Raman spectroscopy, in particular, has been used in the study of 2D antiferromagnetic materials: it has been found that the magnetic ordering often correlates with the changes in the Raman spectrum [1], and low-energy magnons can be detected through low-frequency Raman scattering measurements [2]. NiPS₃ is an XXZ-type 2D van der Waals antiferromagnetic material with the monoclinic crystal structure, which has been extensively studied: the suppression of the long-range order in the monolayer limit has been reported, and a ‘coherent’ magnetic exciton state has been discovered [3]. More recent studies reveal that the bulk crystal structure may not be conserved in the few-layer limit, and complex domain structures exist. Raman spectroscopic imaging, in combination with electron microscopy provides a detailed picture of such domain structures. Furthermore, when few-layer NiPS₃ is stacked on another such piece, the interfacial interaction between the two specimens affects both the phonons and the magnons, implying that the magnetic state is modified. In this talk, I will review recent advances in the study of 2D van der Waals magnetic materials using Raman spectroscopy and discuss outstanding issues.



[1] K. Kim, J.-U. Lee, H. Cheong, Nanotechnology 30, 452001 (2019).

[2] W. Na, et al., ACS Nano 18, 20482 (2024).

[3] S. Kang, et al., Nature 583, 785 (2020).