Book Chapter "Smart Materials for Smart Living"

ISBN: 978-153612280-0;978-153612269-5

Ceramic samples of La_1-xSr_xMn_0.5Ni(Co)_0.5O₃ with perovskite structure are considered to be promising functional materials due to their intriguing magnetic and magnetoresistive properties. Physical properties of these compounds dependent on their structural parameters and electron configuration of the related transition metal ions. These compounds have been thoroughly studied by neutron diffraction technique, magnetometry and magnetoresistance measurements. The obtained results have allowed us to determine the evolution of the structural parameters of the compounds upon chemical substitution while their crystal structure remains to be rhombohedral up to the dopant concentration of 20%, in the case of the Co-doped compounds further increase of Sr content favors a stabilization of cubic structure. The substitution by strontium ions leads to a degradation of long-range ferromagnetic order attributed to both initial compounds towards either antiferromagnet and spin glass state in the case of Ni and Co containing samples respectively. All the compounds are semiconductors and exhibit large magnetoresistance which gradually increases with temperature decreasing, an increase of strontium concentration leads to a decrease of magnetoresistance effect. The obtained results testify that the chemical substitution leads to an increase in the average oxidationstate of Ni and Co ions from 2⁺ into 3⁺ one while manganese ions remain 4⁺ oxidation state. The character and stability of the superexchange interaction between pairs of Co, Mn and Ni ions via oxygen ion which govern magnetic properties of the compounds are discussed depending on the oxidation state and electron configuration of the respective transition metal ions and structural peculiarities of the compounds. © 2017 Nova Science Publishers, Inc.