Submillimeter spectroscopy and magnetic study of La1-xSrxMnO3 ferromagnets

Submillimeter dynamic properties (dielectric permittivity epsilon'(nu,T), dynamic conductivity sigma'(nu,T)) at frequencies nu = 3-20 cm(-1) as well as static ones (magnetization, AC magnetic susceptibility, resistance and magnetoresistance) of the La1-xSrxMnO3 (x = 0.1, 0.175, 0.2 and 0.3) ferromagnets have been studied at temperatures between 5 K and 400 K. PL sharp increase of sigma'(nu,T) was observed near the Curie temperature at a metal-semiconductor transition in La0.825Sr0.17MnO3 .sigma'(nu,T) was described by the Drude model and was equal or slightly greater than its static value. In La0.9Sr0.1MnO3 sigma'(nu,T) was considerably greater than the static value, because not only the Drude-like charge carriers contribute to the dynamic conductivity sigma'(nu,T) but also the crystal lattice. A significant anisotropy of epsilon'(T) was observed for different crystallographic directions. A jump of epsilon'(T) as well as anomalies in the AC magnetic susceptibility were found at T = 100-120 K in La0.9Sr0.1MnO3 which indicate the existence of an additional phase transition (polaron ordering) besides the magnetic transition at 160 K. (C) 1998 Elsevier Science B.V. All rights reserved.