Synthesis and magnetic properties of colloidal superparticles assembled by Mn3O4 octahedral nanocrystals

Abstract Mn3O4 octahedral nanocrystals with a size of about 10∼12 nm are synthesized and further assembled into colloidal superparticles via a microemulsion-based approach. The synthesized typically colloidal superparticles have a spherical shape with an average diameter of about 115 nm, and their sizes are affected by the surfactant concentration and ultrasonic time. The nanocrystals in the typical superparticles have more compact configuration with reduced interparticle distance compared with un-assembled powders. Magnetic measurements reveal that although the typical superparticle sample and two un-assembled powder samples have basically the same Curie temperature, the colloidal superparticles exhibit a higher blocking temperature. In addition, a larger coercivity of about 9881Oe is also observed at 5 K for the colloidal superparticles. The interface pinning effect to the flipping of spins due to the formation of spherical superparticles may need to be taken into account for the enhanced coercivity.