Substitution induced magnetic phase transitions and related electrical conduction mechanisms in LaFeO3 nanoparticle.

The effects of disorder on the magnetic phases as well as on the conduction process are extensively studied in LaFeO₃ nanoparticles in a wide field and temperature ranges. The disorder induced by Na in LaFeO₃ alters its robust magnetic phase to the coexistence of distinctly different magnetic orders. The phase purity of the samples, which plays an important role, is detected by synchrotron x-ray diffraction. Detailed magnetic measurements are carried out to investigate the evolution of phases due to substitutions. The samples show the coexistence of a superparamagnetic phase along with a weak ferromagnetic phase, and the ratio of the two distinct phases varies with substitutions. The Mössbauer measurement supported the said magnetic phases in the samples. The X-ray photoelectron spectroscopy analysis clarifies the simultaneous presence of Fe³⁺ and Fe⁴⁺ due to Na⁺ incorporation. Furthermore, the electrical conduction is found to be greatly influenced by such substitutional disorder. From the dielectric measurement, a p-type polaronic conduction mechanism is found in 25% Na incorporation, which is mainly due to the hole hopping between Fe⁴⁺ and Fe³⁺ states. The semicircles in the whole temperature range in the Cole–Cole plots of impedance and modulus spectra are the co-contribution of the grain and the grain boundary effect in the conduction process. [ABSTRACT FROM AUTHOR]