Properties of La–Sr Manganites with Combined Substitution of Different Valence Ions for Strontium and Manganese

Resumo

Experimental data on structural, magnetic, and electrical features of manganites of the system La_0.65Sr_0.35–cCecMn_{1 – x}Zn_xO_{3 + γ} (c = 0, 0.05; x = 0, 0.05, 0.10), synthesized by ceramic processing, are reported. Part of the samples were annealed under conditions that yield stoichiometric oxygen content. The samples obtained are of rhombohedral structure, but contain the impurity of the CeO₂ phase. The introduction of cerium and zinc leads to a decrease in the unit cell volume of the rhombohedral phase. Cerium does not substantially affect the magnetization and Curie point of the initial samples. The width of the “ferromagnetic–paramagnetic” transition temperature interval rises after annealing, especially in manganite with high zinc content. Initial and annealed samples of composition with c = 0.05, x = 0.10 exhibit the phase transition “metal–semiconductor” at temperatures of about 219 K and 200 K, respectively. All other manganites possess a metallic character of conductivity in the range of 100–300 K. The maximum absolute value of magnetoresistance reaches 52%. The approaches to the interpretation of experimental results are discussed.