Temperature- and magnetic field-dependent Raman spectroscopy of layered, antiferromagnetic FePS₃

J. A. BUCHMAN, J. R. SIMPSON, Towson University, Towson, MD 21252, T. T.MAI, K. F. GARRITY, A. R. HIGHT WALKER, National Institute of Standards and Technology (NIST), Gaithersburg, MD20899, R. VALDE ́S AGUILAR, The Ohio State University, Columbus,OH 20899 —The recent discovery that van der Waals-bonded magnetic materials retain long range magnetic ordering down to a single layer stimulates a thorough Raman spectroscopic study of one such material, FePS₃, a large spin ($S = 2$) Mott insulator where the Fe atoms form a honeycomb lattice. Bulk FePS₃ was shown to be a quasi-2D Ising antiferromagnet, with additional features in the Raman spectra emerging below the Neel temperature (T_N ~ 120K). Previous magneto Raman measurements[1] demonstrated that one of these Raman-active modes below T_N is a magnon. Additional low-frequency, Raman-active modes demonstrate unusual temperature dependance, which we measure using a triple grating Raman spectrometer. In this process, we design and implement an entrance optical path, an alignment procedure, and an excitation light clean up scheme. Furthermore, we use group theory analysis of the polarization-dependent spectra to identify symmetry designations of Raman-active modes. Finally, we compare our spectra with predictions from density functional theory to discuss the origin and anomalous temperature dependence of additional low-frequency Raman-active modes.

[1] A. McCreary et al., Phys. Rev. B 101, 064416 (2020).