Low temperature synthesis of Mn3O4 polyhedral nanocrystals and magnetic study

Manganese oxide (hausmannite) polyhedral nanocrystals were prepared by a microwave-assisted solution-based method using Mn(CH3COO)2 and (CH2)6N4 at 80 °C. The as-prepared Mn3O4 nanocrystals were characterized by means of X-ray diffraction, field-emission transmission electron microscopy, field-emission scanning electron microscopy and Raman spectrum. Mn3O4 polyhedral nanocrystals prepared by microwave heating at 80 °C for 60 min were of cubic and rhombohedral shapes with the edge lengths in the range of 15–40 nm. Mn3O4 nanocrystals grew following the Ostwald ripening mechanism with increasing reaction time. High-resolution transmission electron microscopy and selected area electron diffraction confirm that the as-obtained polyhedral nanocrystals were single-crystalline. The magnetic behavior of Mn3O4 nanocrystals was studied. Mn3O4 nanocrystals show an obvious ferromagnetic behavior at low temperatures. The magnetic behavior of Mn3O4 nanocrystals was sensitive to crystal size. Ferromagnetic onset temperatures (Tc) of samples 1 and 3 are 40.6 and 41.1 K, respectively, lower than that observed for bulk Mn3O4 (42 K).