Raman Spectra of Magnetic Garnet Crystals with and Without Magnetic Fields

Overview

A lingering question in the field of laser science is how does light carrying spin and orbital angular momentum interact with quasi particles in solid states systems? In magnetic crystals there are optical phonons and magnons. Our study sought to explore this relationship by observing the effect of a magnetic field B on the Raman spectra from optical phonons and magnons in three magnetic garnets: Tb3Fe5O12, Tb3Fe5-xGaxO12, and Gd3Fe5O12. We took the spectra at interval magnetic field strengths ranging from 0.30-3.6 Tesla to observe changes caused by the magnon, optical photon, and polariton excitations within the crystals. The key quasi particles in garnets are: Optical phonons, which are polar vibrations of the atomic lattice; and magnons, which are spin waves (alignment of atomic spin vectors). Both can be excited by a Raman scattering process. Since the energy required to change the alignment of a spin vector depends on the strength of the magnetic field B, it is expected that a magnetic field will change the spectrum of the magnons. In addition, we planned to take spectra with circularly polarized light in order to see if the spin polarization affects the magnetic interaction of the light and the sample. We took hundreds of spectra and each set of spectra narrowed in on specific criteria that we believed would yield results. While many spectra showed no changes, some had minor changes that guided our spectrum parameters and experimental set-up. We were able to identify specific peaks that fluctuated due to the varied magnetic field, but we need to take more spectra (with and without B and orbital (L) and spin (S) angular momentum) in order to have conclusive results. This study laid the foundation for the future of optical communications systems, which only operate within a specific bandwidth, but the addition of orbital and spin angular momentum could potentially encode exponentially more information with S and L. There is a lot to do in these materials in the future to firm up our observation.

Competition history

• AJAS 2018 Category not listed

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