Size-control and size-selection at the nanosize level: Production of CoFe2O4 nanoparticles of unusual high coercivity at room temperature
C.N. Chinnasamy, B. Jeyadevan, O. Perales-Perez, K. Shinoda, K. Tohji, A. Kasuya
University of Puerto Rico, Faculty of Engineering, Department of General Engineering-Materials Science and Engineering, PR
Keywords: nanoparticles, size-controlled synthesis, size-selective separation, coercivity, cobalt ferrite
Here, we introduce a solution chemistry technique which involves a `seeding step` under conditions where nucleation and growth rates of particles are controlled to produce single domain well-crystallized CoFe2O4 nanoparticles followed by a size-selective separation of the product. Controlling the concentration of CoFe2O4 seeds in aqueous solution enhanced the room temperature coercivity of produced nanoparticles, and it reached the maximum of 2.29 kOe for the seed concentration of 3.33 g/l of solution.The particles produced under optimum concentration of seeds were size classified at nanometer level after coating the particles with surfactant and particle size dependent coercivity was studied in detail. The cobalt ferrite particles of 40 nm exhibited hither to reported coercivity value of 4.65 kOe, which was close to the theoretical value of 5.3 kOe, a moderate magnetization of 50 emu/gm and squareness ratio of 0.66 at room temperature. An advantage of seeding method is the ability to produce large amounts of ferrite in an economical and viable way for magnetic recording applications. The synthesis technique, which was key to the success of producing highly crystalline cobalt ferrite with unusually high coercivity, could be extended to the synthesis of ceramic and semiconductor single domain particles of nanometer size with properties close to the theoretical predictions.
NSTI Nanotech 2003 Conference Technical Program Abstract