Temperature- and Magnetic Field-Dependent Raman Spectroscopy of Layered, Antiferromagnetic FePS3

Abstract

The recent discovery that van der Waals-bonded magnetic materials retain long range magnetic ordering down to a single layer[1,2] 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 (TN ~ 120 K). Using temperature- and magnetic field-dependent Raman spectroscopy as an optical probe of magnetic structure, we demonstrate[3] that one of these Raman-active modes (ψ4) below TN is a magnon with a frequency of ~ 3.7 THz (~122 cm-1). Contrary to previous work[4], which interpreted this feature as a phonon, our Raman data[3] shows the expected frequency shifting and splitting of the magnon as a function of temperature and magnetic field, respectively, were we find the g-factor ~2. Other Raman-active modes emerging below TN are attributed to zone-folded phonons in the antiferromagnetic state. The anomalous temperature dependence of these modes along with an analysis of temperature-dependent magnetization data, suggests a persistence of short-range magnetic order above TN.