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, 10–1, 105 Pa, respectively. All synthesized manganites have rhombohedral structure and are characterized by small value of microdistortions, 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+(3d 6) 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. Mechanisms of the formation of current-voltage characteristics of various types are considered.