  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 cm^{-1}
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 T_{N}, which we attribute to strong coupling between magnetic and
vibrational excitations near the zone boundary.
