Ultrasonic-Assisted Synthesis of Colloidal Mn3O4 Nanoparticles at Normal Temperature and Pressure

A facile direct synthesis has been developed to prepare colloidal Mn3O4 nanoparticles with diameters of about 5−10 nm at normal temperature and pressure by an ultrasonic-assisted method in the absence of any additional nucleation and surfactant. High-resolution transmission electron microscopy observations revealed that the as-synthesized nanoparticles were single crystals. The magnetic properties of the samples were investigated in detail. The superconducting quantum interference device (SQUID) results showed that Mn3O4 nanoparticles exhibited ferromagnetic behavior at low temperature (40 K).