Fеatures of exchange interactions of the B-sublattice ions in the La 0,5 Sr 0,5 Co 1–x Ni x O 3–d system

A comprehensive study of the crystal structure, magnetic and magnetotransport properties of the La 0.5 Sr 0.5 Co 1–x Ni x O 3–d  cobaltite system (x = 0.1–0.16) was carried out. The X-ray measurement results indicate that the unit cell of all solid solutions of the system is cubic and is described by the space group Pm3m. It is found that with an increase in the 540 Doklady of the National Academy of Sciences of Belarus, 2021, vol. 65, no. 5, рр. 539–545 Ni content, the Curie temperature (TC) decreases from 230 to 180 K, as well as magnetization values. The magnetic transition is blurred across the field. The iodometric studies show that the concentration of Co 4+ ions in all samples does not exceed 35 %. The chemical substitution of Co ions by Ni ones does not result in significant modification of the unit cell parameters, which may indicate a spin crossover of Co ions. The temperature dependence of resistivity is metallic in character, which indicates the stability of the main conducting ferromagnetic phase. The nature of exchange interactions of different signs between B-sublattice ions completely determines the behavior of the system. An increase in the content of Ni ions leads both to decrease the component of ferromagnetic exchange interactions between Co 3+ ions in the intermediate spin state and to increase the fraction of antiferromagnetic and weaker ferromagnetic interactions. In addition, presumably the Co 4+ ion can stabilize the high spin state of the closestCo 3+ ion and in the next two coordination spheres it can stabilize the Co3+ ion in the low spin state, i. e. the ferromagnetic complexes Co 4+ –Co 3+ (HS) are shielded by the diamagnetic shell of low spin Co3+ ions, which results in decreasing the magnetization values.