We studied electron spin resonance (ESR) spectra of La_0.7A′_0.3MnO₃ (A′=Sr, Ba, Pb, and Cd) perovskites in a large range of temperature, from their Curie temperature to ∼500 K. Asymmetrical EPR signals at temperatures T_C < T < T_min, due to FM correlations, became Lorentzian at T {greater than or slanted equal to} T_min, where T_min is the temperature corresponding to the narrowest ESR linewidth. The ESR linewidth vs. temperature, ΔH(T), in the region T > T_min well fits to the model of adiabatic hopping motion of small polarons Δ H ( T ) = Δ H₀ + ( a / T ) exp ( - E_a / k_B T ), where E_a and k_B are the activation energy and the Boltzmann factor, respectively; ΔH₀ and a are constants. It is worth noticing that, in this temperature range, the Lande factor g for the samples is about 2.00, indicating spin-spin interaction among electrons of Mn³⁺ and Mn⁴⁺ ions playing an important role. © 2006 Elsevier B.V. All rights reserved.

Phan T.L., Tho N.D., Bau L.V., Phuc N.X., Yu S.C.

654.pdf    Gửi cho bạn bè

Từ khóa : Activation energy; Electrons; Lanthanum compounds; Manganese compounds; Mathematical models; Paramagnetic resonance; Thermal effects; Adiabatic hopping motion; Boltzmann factor; Manganites; Perovskite