Influence of structure defects on functional properties of magnetoresistance (Nd0.7Sr0.3)1−xMn1+xO3 ceramics

X-ray powder diffraction, resistance, magnetic susceptibility, magnetization, nuclear magnetic resonance (NMR) and magnetoresistance measurement methods were used to study the influence of excess manganese on structure defects and functional properties of (Nd0.7Sr0.3)1−xMn1+xO3 ceramics annealed at 1200 and 1500 °C. It was established that, with an increase in both excess manganese and annealing temperature, the perovskite structure defects, resistance and activation energy increase, while the magnetic susceptibility and fraction of ferromagnetic phase decrease. The occurrence of nanostructured planar clusters is shown to be caused by the presence of excess manganese. Broad asymmetric 55Mn NMR spectra are indicative of both the high-frequency electron Mn3+ ↔ Mn4+ exchange and the uneven distribution of ions and vacancies. The magnetoresistance effect near the Curie temperature increases with increasing annealing temperature and excess manganese content. Magnetic phase diagrams characterizing a strong correlation between the composition, structural defects and functional properties in manganese–neodymium perovskites were constructed.