Influence of A-site substitution on the EPR parameters of La0.7A′0.3MnO3 0.3 (A′ = Sr, Ba) compounds

In this paper, we investigate in detail influences of A-site substitution on the EPR parameters for La(0.7)rSr(0.3)MnO(3) (LSM) and La0.7Ba0.3MnO3 (LBM) compounds by means of electron paramagnetic resonance (EPR) study. Magnetization and resistivity measurements were also performed. The Curie temperature T-C is 365 and 322 K for LSM and LBM, respectively. In the whole temperature range studied, metallic behavior was observed. The minimum linewidth Delta H-min is 402 and 378 Oe for LSM and LBM, respectively. Temperature dependences of the EPR linewidth Delta H-pp(T) for the samples were analyzed by using the model of adiabatic hopping motion of small polarons, Delta H-pp(T) = Delta H-0 + (A/T) exp(-E-a/k(B)T). The activation energies E-a((1)) and E-a((2)), obtained from Delta H-pp(T) and EPR intensity I(T) data, are different. At temperatures T > T-min, the Lande factor of both samples is the same (g approximate to 2), indicating that spin-spin interactions among electrons of Mn3+ and Mn4+ ions play a main role.