Structural, magnetic and electrical characteristics of La – Sr manganites depending on electronic configuration of manganese substituents and oxygen concentration

Manganites La0.7Sr0.3Mn0.9Fe0.05Me0.05O3+γ (Me = Sc, Co) with different oxygen content (γ < 0, γ = 0, γ > 0) were synthesized. Corresponding values of γ were obtained by annealing of sintered samples at different oxygen pressures: 10–8 Pa, 10–1 Pa, 105 Pa, respectively. All synthesized manganites have rhombohedral structure and are characterized by small value of micro-distortions, which is associated with the formation of modulated structures. Microstructure of the samples is quite dense, with an average crystallites diameter of 3.9 ± 1.6 µm for scandium-containing manganite and 3.1 ± 1.3 µm for (Fe,Co)-substituted manganite. Unit cell parameters and electromagnetic characteristics of the latter indicate the presence of Co3+(3d6) ions in its composition. (Fe,Sc)-containing manganites have lower magnetization values, Curie points and a significantly lower metal-semiconductor transition temperature compared to those containing iron and cobalt. Current-voltage (I – V) characteristics of La0.7Sr0.3Mn0.9Fe0.05Sc0.05O3+γ and La0.7Sr0.3Mn0.9Fe0.05Co0.05O3+γ manganites with negative deviation from oxygen stoichiometry and stoichiometric exhibit negative differential resistance of S-type in certain temperature ranges, and I – V characteristics of (Fe,Co)-substituted manganite in magnetic field contain two S-shaped sections. Threshold switching fields and maximum values of negative differential resistance modulus of I – V characteristics at different temperatures are determined. (Fe,Sc)-substituted manganite with an excess oxygen content at 190 – 200 K exhibits voltage stabilization effect. I – V characteristic of (Fe,Co)-substituted manganite annealed in oxygen does not contain the sections with negative differential resistance.