Date of Award


Degree Name

Master of Science




Harikrishnan H. Nair


In olivine chalcogenide Mn2SiX 4 (X = S, Se) compounds, the Mn lattice produces a sawtooth, which is of critical significance in magnetism due to the potential for manifesting at bands in the magnon spectrum, a crucial component in magnonics. The compounds Mn2SiS4 and Mn2SiSe4 in Mn2SiX 4 family undergo antiferromagnetic phase transitions at T â?? 85 K and â?? 66 K, respectively, as determined from the specific heat, Cp(T). The average and local crystal structuresare determined using synchrotron X-ray, neutron diffraction, and X-ray total scattering data followed by Rietveld and pair distribution function (PDF) analysis. It is found from PDF that the Mn triangle that constitutes the sawtooth is isosceles in Mn2SiS4 whereas it is nearly equilateral in Mn2SiSe4. The magnetic phase transitions in Mn2SiX 4 seen in bulk measurements are confirmed using neutron diffraction in this work, and the magnetic structures accurately estimated. We find that the Mn spins adopt a ferromagnetic alignment on the sawtooths in both Mn2SiS4 and Mn2SiSe4 but along different crystallographic directions. By following the thermal evolution of the refined magnetic moment at the Mn site, obtained from refining the neutron diffraction data, the transition temperatures are accurately determined as TN(S) = 83(2) K and TN(Se) = 70.0(5) K. The magnetic space groups are determined as P nma and P nm0a 0 for Mn2SiS4 and Mn2SiSe4, respectively. The magnetic excitations studied using inelastic neutron scattering reveal a magnon excitation with an energy corresponding to 4.5 meV in both the compounds.




Received from ProQuest

File Size

90 p.

File Format


Rights Holder

Melaku Sisay Tafere