Hybridized mode of phonon and spin-cluster excitation in quasi-one-dimensional magnet CoNb2O6

Transmission measurements of far-infrared (FIR) polarized radiation have be en performed in CoNb2O6 sing le crystal. We have observed an absorption lin e at 9.7cm(-1) with a broad band from 9 to 25cm(-1) which should Le attribu ted to the I,phonon of the lowest frequency below 30 cm(-1) from the lattic e dynamical analysis. As the temperature is decreased below 20 Ii and also as the magnetic field is apl,lied up to GT, the absorption line will tie ba nd was intensively studied in magnetic fields as well as the various temper atures by using polarized FIR radiation field E parallel to the b- and c-ax is. From the study., the Land is attributed tu the spill-cluster excitation (SCE) in the Ising-like chain. On tie other hand, the absorption lille als o exhibits the variation as similar as SCE in magnetic fields. It concludes that the absorption lille at 0.7 cm(-1) is the hybridized mode of the B-3u mode of the phonon of the lowest frequency and SCE.