Raman spectra on TDAE-${\mathrm{C}}_{60}$ single crystals

Low-temperature single-crystal Raman spectra are presented for the organic ferromagnetic insulator TDAE-${\mathrm{C}}_{60}$. The mode intensities, line shifts, linewidths, and depolarization ratios are compared with alkali-doped fullerene materials and with pure ${\mathrm{C}}_{60}$. A comparison of visible laser light excited spectra (${\mathrm{E}}_{\mathrm{exc}}$=2.41 eV) with infrared excited Raman measurements (${\mathrm{E}}_{\mathrm{exc}}$=1.17 eV) shows a selective resonance effect whereby in the visible spectra, a frequency shift of only the tangential modes is observed, while in the infrared measurement, which is resonant with the ${\mathrm{t}}_{1\mathrm{u}}$-${\mathrm{t}}_{1\mathrm{g}}$ electronic transition, the radial modes are also observed to shift. The effect is attributed to Raman resonance with different relaxed states of ${\mathrm{C}}_{60}^{\mathrm{-}}$.