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Magnon spectra and strong spin-lattice coupling in magnetically frustrated MnB2 O4 (B=Mn,V): Inelastic light-scattering studies

  • Author(s): Gleason, SL
  • Byrum, T
  • Gim, Y
  • Thaler, A
  • Abbamonte, P
  • Macdougall, GJ
  • Martin, LW
  • Zhou, HD
  • Cooper, SL
  • et al.

The ferrimagnetic spinels MnB2O4 (B=Mn,V) exhibit a similar series of closely spaced magnetic and structural phase transitions at low temperatures, reflecting both magnetic frustration and a strong coupling between the spin and lattice degrees of freedom. Careful studies of excitations in MnB2O4 (B=Mn,V), and the evolution of these excitations with temperature, are important for obtaining a microscopic description of the role that magnetic excitations and spin-lattice coupling play in the low-temperature phase transitions of these materials. We report an inelastic light (Raman) scattering study of the temperature and magnetic-field dependences of one- and two-magnon excitations in MnV2O4 and Mn3O4. We observe a pair of q=0 one-magnon modes at 74 and 81 cm-1 in MnV2O4, which is in contrast with the single 80-cm-1 q=0 magnon that has been reported for MnV2O4 based on previous neutron-scattering measurements and spin-wave calculations. Additionally, we find that the two-magnon energy of MnV2O4 decreases ("softens") with decreasing temperature below TN, which we attribute to strong coupling between magnetic and vibrational excitations near the zone boundary. © 2014 American Physical Society.

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