Influence of a-site substitution on the EPR parameters of La/sub 0.7/A'/sub 0.3/MnO/sub 3/ (A'= Sr, Ba) compounds

In this paper, we investigate in detail influences of A-site substitution on the EPR parameters for La/sub 0.7/Sr/sub 0.3/MnO/sub 3/ (LSM) and La/sub 0.7/Ba/sub 0.3/MnO/sub 3/ (LBM) compounds by means of electron paramagnetic resonance (EPR) study. Magnetization and resistivity measurements were also performed. The Curie temperature T/sub C/ is 365 and 322 K for LSM and LBM, respectively. In the whole temperature range studied, metallic behavior was observed. The minimum linewidth /spl Delta/H/sub min/ is 402 and 378 Oe for LSM and LBM, respectively. Temperature dependences of the EPR linewidth /spl Delta/H/sub pp/(T) for the samples were analyzed by using the model of adiabatic hopping motion of small polarons, /spl Delta/H/sub pp/(T)=/spl Delta/H/sub 0/+(A/T)exp(-E/sub a//k/sub B/T). The activation energies E/sub a//sup (1)/ and E/sub a//sup (2)/, obtained from /spl Delta/H/sub pp/(T) and EPR intensity I(T) data, are different. At temperatures T>T/sub min/, the Lande factor of both samples is the same (g/spl ap/2), indicating that spin-spin interactions among electrons of Mn/sup 3+/ and Mn/sup 4+/ ions play a main role.