Light scattering from electronic and magnetic excitations in α′-NAV2O5

We present the Raman scattering spectra of alpha'-NaV2O5 single crystal. In the high-temperature phase, besides phonon modes, there are three broad continuum-hire features observed at energies centred at 160, 603 and 2400 cm(-1) (T = 100 K) which are described as an indication of d-d electronic transitions of V ions. Due to the magnetic ordering at T < 34 K, appearing as a consequence of charge ordering, these paramagnetic bands split into several excitons with energies of 65, 106, 200, 2000 and 3000 cm(-1). The assigning of the lowest-energy mode at 65 cm(-1) as the one-magnon mode, as well as the onset of the magnetic continuum at 126 cm(-1), is done on the basis of Monte Carlo calculation of excited states of a Heisenberg dimerized Hamiltonian without frustration. A good agreement between the measured and calculated magnetic excitation energies for delta = 0.047 and J = 455 K has been found. Other lines in the low-temperature Raman spectra represent phonons becoming Raman active due to the Brillouin-zone-folding effect.