Quasi-two-dimensional magnon identification in antiferromagnetic<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>FeP</mml:mi><mml:msub><mml:mi mathvariant="normal">S</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>via magneto-Raman spectroscopy
Amber McCreary, Jeffrey R. Simpson, T. Thuc, R. D. McMichael, Jason E. Douglas, Nicholas P. Butch, Cindi L. Dennis, Rolando Valdés Aguilar, Angela R. Hight Walker
Abstract
Recently it was discovered that van der Waals bonded magnetic materials retain long range magnetic ordering down to a single layer, opening many avenues in fundamental physics and potential applications of these fascinating materials. One such material is $\mathrm{FeP}{\mathrm{S}}_{3}$, a large spin $(S=2)$ Mott insulator where the Fe atoms form a honeycomb lattice. In the bulk, $\mathrm{FeP}{\mathrm{S}}_{3}$ has been shown to be a quasi-two-dimensional-Ising antiferromagnet, with additional features in the Raman spectra emerging below the N\'eel temperature $({T}_{\mathrm{N}})$ of approximately 120 K. Using magneto-Raman spectroscopy as an optical probe of magnetic structure, we show that one of these Raman-active modes in the magnetically ordered state is actually a magnon with a frequency of $\ensuremath{\approx}3.7\phantom{\rule{0.16em}{0ex}}\mathrm{THz}\phantom{\rule{4pt}{0ex}}(122\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1})$. Contrary to previous work, which interpreted this feature as a phonon, our Raman data shows the expected frequency shifting and splitting of the antiferromagnetic magnon as a function of temperature and magnetic field, respectively, where we determine the $g$ factor to be $\ensuremath{\approx}2$. In addition, the symmetry behavior of the magnon is studied by polarization-dependent Raman spectroscopy and explained using the magnetic point group of $\mathrm{FeP}{\mathrm{S}}_{3}$.