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

In this paper, we investigate in detail influences of A-site substitution on the EPR parameters for La_0.7Sr_0.3MnO₃ (LSM) and La_0.7Ba_0.3MnO₃ (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 ΔH_min is 402 and 378 Oe for LSM and LBM, respectively. Temperature dependences of the EPR linewidth ΔH_pp(T) for the samples were analyzed by using the model of adiabatic hopping motion of small polarons, ΔH_pp(T)=ΔH₀+(A/T)exp(-E_a/k_BT). The activation energies E_a⁽¹⁾ and E_a⁽²⁾, obtained from ΔH_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≈2), indicating that spin-spin interactions among electrons of Mn³⁺ and Mn⁴⁺ ions play a main role.