Structure defects, phase transitions, magnetic resonance and magneto-transport properties of La0.6-xEuxSr0.3Mn1.1O3-δ ceramics

Structure and its defects, magnetic resonance and magneto-transport properties of La0.6-xEuxSr0.3Mn1.1O3-delta magnetoresistive ceramics were investigated by x-ray diffraction, thermogravimetric, resistance, magnetic, Mn-55 NMR and magnetoresistance methods. It was found that isovalent substitution of lanthanum by europium A-cation of a smaller ionic radius increases the structural imperfection and leads to a symmetry change from the rhombohedrally distorted perovskite structure of R (3) over barc symmetry to the pseudocubic type. It was shown that the real structure contains anionic and cationic vacancies, the concentrations of which increases with the Eu concentration and the sintering temperature t(ann). A decrease in the temperature of the metal-semiconductor T-ms and ferromagnetic-paramagnetic T-C phase transitions as well as an increase in the resistivity rho and the activation energy E-a with increasing x are due to an increase in vacancy concentration, which weakens the high-frequency electron double exchange Mn3+ <-> O2- <-> Mn4+. The crystal structure of the compositions x = 0 and 0.1 contains nanostructured planar clusters, causing anomalous magnetic hysteresis at T = 77 K. Broad asymmetric Mn-55 NMR spectra confirm high-frequency electron double exchange Mn3+(3d(4))<-> O2-(2p(6))<-> Mn4+(3d(3)) and indicate inhomogeneity of the manganese environment due to the surrounding ions and vacancies. The effective local fields of the hyperfine interaction H-HF at Mn-55 nuclei have been calculated by decomposing asymmetric NMR spectra into three Gaussian components. The constructed experimental phase diagram of the magnetic and conducting states of the La0.6-xEuxSr0.3Mn1.1O3-delta ceramics revealed strong correlation between the composition, structural imperfection, phase state, and magneto-transport properties of rare-earth manganites. Published by AIP Publishing.