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, re sistance 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 Cu rie temperature at a metal-semiconductor transition in La0.825Sr0.17Mn O3 .sigma'(nu,T) was described by the Drude model and was equal or sli ghtly greater than its static value. In La0.9Sr0.1MnO3 sigma'(nu,T) wa s considerably greater than the static value, because not only the Dru de-like charge carriers contribute to the dynamic conductivity sigma'( nu,T) but also the crystal lattice. A significant anisotropy of epsilo n'(T) was observed for different crystallographic directions. A jump o f epsilon'(T) as well as anomalies in the AC magnetic susceptibility w ere found at T = 100-120 K in La0.9Sr0.1MnO3 which indicate the existe nce of an additional phase transition (polaron ordering) besides the m agnetic transition at 160 K. (C) 1998 Elsevier Science B.V. All rights reserved.