Optical, electrical and magnetic properties of nanostructured Mn3O4 synthesized through a facile chemical route

• Synthesis of phase pure nanostructured Mn3O4 through a facile chemical route.
• Presence of Mn4+ ions established by Raman, UV–visible and X-ray photoelectron spectroscopy.
• Enhancement of DC conductivity by five orders of magnitude compared to that of single crystalline Mn3O4.
• Slight increase in Curie temperature due to the presence of a disordered surface.
• Magntization following the Langevin relation due to the ferromagnetic core and linear dependence due to disordered surface spins.

Nanostructured Mn3O4 sample with an average crystallite size of ∼15 nm is synthesized via the reduction of potassium permanganate using hydrazine. The average particle size obtained from the Transmission Electron Microscopy analysis is in good agreement with the average crystallite size estimated from X-ray diffraction analysis. The presence of Mn4+ ions at the octahedral sites is inferred from the results of Raman, UV–visible absorption and X-ray photoelectron spectroscopy analyzes. DC electrical conductivity of the sample in the temperature range 313–423 K, is about five orders of magnitude larger than that reported for single crystalline Mn3O4 sample. The dominant conduction mechanism is identified to be of the polaronic hopping of holes between cations in the octahedral sites. The zero field cooled and field cooled magnetization of the sample is studied in the range 20–300 K. The Curie temperature for the sample is about 45 K, below which the sample is ferrimagnetic. A blocking temperature of 35 K is observed in the field cooled curve. It is observed that the sample shows hysteresis at temperatures below the Curie temperature with no saturation, even at an applied field (20 kOe). The presence of an ordered core and disordered surface of spin arrangements is observed from the magnetization studies. Above the Curie temperature, the sample shows linear dependence of magnetization on applied field with no hysteresis characteristic of paramagnetic phase.

Cation vacancies lead to the presence of Mn4+ ions which alter the optical response, electrical conductivity and magnetic response of nanostructured Mn3O4.Figure optionsDownload as PowerPoint slide