GIANT PHONON SOFTENING IN FERROMAGNETIC LAMNO_(3+δ)

摘要

High quality single crystals of LaMnO_(3+δ) with δ =0.071, 0.085, 0.092, 0.097, 0.125 that extend from antiferromagnetic insulating (δ = 0.071, T_N = 128 K) to ferromagnetic metallic state (δ =0.125, T_C = 248 K) have been investigated by polarized Raman light scattering. A giant softening up to 30 cm~(-1) of the 490- and 620-cm~(-1) phonon modes has been observed below the Curie temperature. We interpret this phenomenon as a manifestation of an orbital fluctuating state which exists in a wide temperature range in ferromagnetic LaMnO_(3+δ).