Magneto-optical study on alpha '-NaV2O5 in high magnetic fields

Far-infrared magneto-optical studies were performed on alpha'-NaV2O5 up to 15 T. Magnetic absorption modes were observed at 68, 106 and 124 cm(-1) bel ow the critical temperature, T-C = 34K, in E parallel toc configuration, an d they exhibit softening towards T-C. Neither shifting nor broadening of th ese modes was observed in the presence of the magnetic held up to 15T, whic h suggests that these modes are caused by the excitation to the magnetic bo und states. Besides the sharp absorption modes, a broad absorption band was observed on the spectra of E parallel toc. Its oscillator strength shows a n anomalous decrease at T-C, which would be related to charge disproportion . (C) 2001 Elsevier Science B.V. All rights reserved.