Polek T. Effect of substitution and mechanical stresses on magnetoresistive and resonance properties of lanthanum manganites

The thesis is aimed at research of the influence of chemical substitutions and substrate-induced mechanical stresses on magnetoresistive and resonance properties of lanthanum manganites. To solve the problem, the magnetic, electric, magnetoresistive and X-ray research methods in combination with electron spin resonance technique have been used. By employing a direct experimental method of electron spin resonance, it has been shown that the transition from paramagnetic to ferromagnetic state in La1-xBixMnO3+ system occurs through a gradual redistribution of the volumes of paramagnetic and ferromagnetic regions. Comprehensive study of La0,775Sr0,225Mn1-xSnxO3 system have resulted in an unambiguous conclusion that by tin doping of manganites, the Sn4+ ions substitute for Mn4+ ions. It has been shown that the type of a substrate strongly affects the electrical properties of the films of La0,6Sr0,2Mn1,2O3 substituted manganites when their thickness becomes less than 20 nm.