Magnetic core-shell particles, each with a single iron oxide nanoparticle core, were prepared by the reverse microemulsion method. By using 1-butanol as a co-surfactant, one can effectively control the particle size ranging from 60 to 185 nm. The mechanism of incorporation of the hydrophobic nanoparticles in the center of a colloidal particle was discussed. The magnetic characteristics of the bare iron oxide nanoparticles and core-shell colloidal particles were studied by SQUID measurements. Superparamagnetic behavior has been found, with a blocking temperature of 200 and 100 K respectively. Under an external magnetic field, the as-prepared colloidal particles can assemble along the field direction to form linear structure. These give us a good chance to control the assembly of these colloidal particles by using an external field. © 2012 Elsevier B.V. All rights reserved.

Magnetic core-shell particles, each with a single iron oxide nanoparticle core, were prepared by the reverse microemulsion method. By using 1-butanol as a co-surfactant, one can effectively control the particle size ranging from 60 to 185 nm. The mechanism of incorporation of the hydrophobic nanoparticles in the center of a colloidal particle was discussed. The magnetic characteristics of the bare iron oxide nanoparticles and core-shell colloidal particles were studied by SQUID measurements. Superparamagnetic behavior has been found, with a blocking temperature of 200 and 100 K respectively. Under an external magnetic field, the as-prepared colloidal particles can assemble along the field direction to form linear structure. These give us a good chance to control the assembly of these colloidal particles by using an external field. © 2012 Elsevier B.V. All rights reserved.