  The discovery of 2-dimensional (2D) materials, such as CrI3, that retain
magnetic ordering at monolayer thickness has resulted in a surge of research in
2D magnetism from both pure and applied perspectives. Here, we report a
magneto-Raman spectroscopy study on multilayered CrI3, focusing on two new
features in the spectra which appear at temperatures below the magnetic
ordering temperature and were previously assigned to high frequency magnons. We
observe a striking evolution of the Raman spectra with increasing magnetic
field in which clear, sudden changes in intensities of the modes are attributed
to the interlayer ordering changing from antiferromagnetic to ferromagnetic at
a critical magnetic field. Our work highlights the sensitivity of the Raman
modes to weak interlayer spin ordering in CrI3. In addition, we theoretically
examine potential origins for the new modes, which we deduce are unlikely
single magnons.
