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Mixed-valence manganites have gained tremendous attention in the scientific research for its colossal magnetoresistance phenomenon. Nevertheless, the study devoted to praseodymiumbased manganites is still limited to date. The present work aims to investigate the grain size effect on sol-gel grown nano-sized Pr0.85K0.15MnO3 (PKMO). The grain size has been modified by heat treatment ranging from 600 °C to 1000 °C. PKMO samples have been studied in detail to elucidate the correlation of spin, charge, orbital and lattice degrees of freedom. The X-ray diffraction analysis revealed that all samples exhibit in single orthorhombic phase with the space group of Pnma (62). The obtained crystallite size and average grain size are in the range of 45-115 nm and 51-210 nm, respectively. The evolution of grains intensively affects the electrical and magneto-transport properties of PKMO. The temperature dependence of the resistivity has been fitted with theoretical expressions in different temperature regimes to investigate their conduction mechanisms. The resistivity exhibits an unusual trend when the grain size increases where a similar pattern also been observed in metal-insulator transition temperature (TMI). This behaviour can be ascribed to the grain size distribution, grain formation and also the occurrence of oxygen vacancies at the grain boundaries. Enhancement of high field magnetoresistance has been discovered below 180 K, whereas low field magnetoresistance is suppressed as the temperature increases and almost vanished at 300 K. The PKMO study demonstrated here is clearly dominated by extrinsic properties (grain evolution) from the evidence of electrical and magneto-transport measurements.

La0.7Sr0.3MnO3 (LSMO) and Nd0.7Sr0.3MnO3 (NSMO) possess excellent colossal magnetoresistance (CMR). However, research work on the neodymium-based system is limited to date. A comparative study between LSMO and NSMO prepared by sol–gel and solid-state reaction methods was undertaken to assess their structural, microstructural, magnetic, electrical, and magneto-transport properties. X-ray diffraction and structure refinement showed the formation of a single-phase composition. Sol–gel-synthesised NSMO was revealed to be a sample with single crystallite grains and exhibited intriguing magnetic and electrical transport behaviours. Magnetic characterisation highlighted that Curie temperature (TC) decreases with the grain size. Strong suppression of the metal–insulator transition temperature (TMI) was observed and attributed to the magnetically disordered grain surface and distortion of the MnO6 octahedra. The electrical resistivity in the metallic region was fitted with theoretical models, and the conduction mechanism could be explained by the grain/domain boundary, electron–electron, and electron–magnon scattering process. The increase in the scattering process was ascribed to the morphology changes. Enhancement of low-field magnetoresistance (LFMR) was observed in nano-grained samples. The obtained results show that the grain size and its distribution, as well as the crystallite formation, strongly affect the physical properties of hole-doped manganites.

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Colossal magnetoresistive (CMR) materials have been widely studied because of their huge potential in spintronic technology. An introduction of secondary phase to the manganite matrix is able to improve the low field magnetoresistance (LFMR). This method is favoured by recent research works as it requires a lower magnetic field compared to intrinsic magnetoresistance. Structural, magnetic properties and magnetotransport properties of polycrystalline (1-x) La0.67Ca0.33MnO3 (LCMO): x TiO2 composites where x = 0.00, 0.05, 0.10, 0.15 and 0.20 were investigated in this work. Polycrystalline La0.67Ca0.33MnO3 (LCMO) was synthesized via sol-gel method and pre-sintered at 800 °C before appending with nano-sized TiO2. All samples are in LCMO phase having an orthorhombic structure with space group Pnma. The crystal structural parameter is studied by using Rietveld refinement. As TiO2 content increases, the magnetization is getting higher as observed via vibrating sample magnetometer (VSM) analysis at room temperature. Magnetotransport properties of the pure LCMO sample have been studied from 80 – 220 K. The LFMR is enhanced as the temperature drops. The results have shown LCMO: TiO2 manganite composite is an excellent candidate for future magnetic sensors and memory devices.