Magneto-Raman Spectroscopy to Identify Spin Structure in Two-Dimensional Materials

Magnetic ordering in the two-dimensional (2D) limit has been one of the most important issues in condensed matter physics for the past few decades. Raman spectroscopy, mapping and imaging  are  powerful non-contact, non-destructive optical probes of fundamental physics in graphene and other related 2D materials, including layered, quantum materials that are candidates for use in the next quantum revolution. An amazing amount of information can be quantified from the Raman spectra, including layer thickness, edge, disorder and doping, grain boundaries, strain, thermal conductivity, magnetic ordering, and unique excitations such as charge density waves. Raman effectively examines the development of the electronic structure and the spin-phonon, electron-phonon, and magnon-phonon interactions as a function of laser energy, temperature, and polarization, which is particularly relevant for quantum materials. The seminar elaborates on using Raman spectroscopy to probe magnetic phenomena in the antiferromagnetic metal phosphorus trichalcogenide family, with highlights on FePS3 and MnPS3.1,2 Using magneto-Raman spectroscopy as an optical probe of magnetic structure, the results show that in FePS3 one of the Raman-active modes in the magnetically ordered state is a magnon with a frequency of 122 cm−1 (~15.1 meV). In addition, the surprising symmetry behavior of the magnon is studied by polarization-dependent Raman spectroscopy and explained using the magnetic point group of FePS3. Finally, the magnetic field- and temperature-dependence of a ferromagnetic 2D material chromium Iodide, CrI3, will be presented.3 The magneto-Raman spectroscopy study will focus on multilayered CrI3 focusing on two additional features in the spectra that appear below the magnetic ordering temperature and were previously assigned to high frequency magnons. Instead, the results shows that these modes are zone-folded phonons. Additionally, striking evolution of Raman spectra with increasing the applied magnetic field perpendicular to the atomic layers uncovers an interlayer ordering changing from antiferromagnetic to ferromagnetic at a critical magnetic field.

 

 

[1] McCreary, A.; Simpson, J. R.; Mai, T. T.; McMichael, R. D.; Douglas, J. E.; Butch, N.; Dennis, C.; Valdes Aguilar, R.; and Hight Walker, A. R. Quasi-two-dimensional magnon identification in antiferromagnetic FePS3 via magneto-Raman spectroscopy, Phys. Rev. B 101, 064416 (2020).

[2] Kim, K.; Lim, S.Y.; Kim, J.; Lee, S; Kim, P; Park, K; Son, S; Park C.H. et al. Antiferromagnetic ordering in van der Waals two-dimensional magnetic material MnPS3 probed by Raman spectroscopy. 2D Mater. 6, 041001 (2019).

[3] McCreary, A.; Mai, T.T.; Utermohlen, F.G. et al. Distinct magneto-Raman signatures of spin-flip phase transitions in CrI3. Nat Commun 11, 3879 (2020).