Magnetic, dielectric, and transport properties of La1-xSrxMnO3 at submillimeter wavelengths

Antiferromagnetic resonance (AFMR), dynamic conductivity, and dielectric pe rmittivity have been studied in the La1-xSrxMnO3 perovskites at a frequency range of nu = 3-33 cm(-1) by the use of a quasi-optical backward-wave-osci llator technique. Two AFMR modes have been observed in LaMnO3 and La0.95Sr0 .05MnO3. Temperature dependencies of their resonance frequencies, linewidth s, and mode contributions to a static magnetic permeability have been obtai ned and corresponding parameters of magnetic interactions have been extract ed. A jump in the dielectric permittivity epsilon'(T) was found at T = 100- 120 K in La0.9Sr0.1MnO3, which indicates the existence of an additional ph ase transition (probably, a polaron ordering) besides the ferromagnetic tra nsition at 170 K. A sharp increase of the dynamic conductivity sigma'(nu, T ) was observed near Curie temperature (285 K) at a metal-semiconductor tran sition in La0.825Sr0.175MnO3, which was slightly smaller than its static va lue. (C) 1998 American Institute of Physics.