Effects of dopants and oxygen non-stoichiometry on thermodynamic and magnetic properties of micro- and nanostructured perovskite type manganites

The aim of the paper is to evidence the effect of the composition and oxygen stoichiometry on the thermodynamic, spin dynamics and magnetic properties of some micro- and nanostructured substituted manganites La_1–xA_xMn_1–yB_yO_3–δ (A=Ca; B=Co, Fe; x=0·33; y=0, 0·02 and 0·04). The partial molar thermodynamic properties of oxygen dissolution in the perovskite phase as well the equilibrium partial pressures of oxygen have been obtained using solid electrolyte electrochemical cells [electromotive force measurement (EMF)] method. The influence of the oxygen stoichiometry change on the thermodynamic properties was examined using the data obtained by a coulometric titration technique coupled with EMF measurements. Using electron paramagnetic resonance spectroscopy, the spin dynamics has been investigated. Particular attention was devoted to the discussion concerning the influence of doping on polaron activation energy E_a and exchange coupling integral J between Mn spins. The results were correlated with the variation of both saturation magnetisation M_s and Curie temperature T_c. The data were discussed in relation to significant changes in the overall concentration of defects. New features related to the modifications in properties connected with the nanocrystalline state were evidenced.