Influence of a magnetic field on the formation of magnetite particles via two precipitation methods.

An experimental investigation is described on the effects of the presence of a magnetic field during the fabrication of magnetite particles. We considered two well-known synthesis methods: that of Massart [IEEE Trans. Magn. 1981, 17, 1247-1248] for the synthesis of nanometer-sized, monodomain particles; and that of Sugimoto and Matijević [J. Colloid Interface Sci. 1980, 74, 227-243.] for the fabrication of micrometer-sized multidomain spherical particles. The latter method was studied with two systems of different ionic compositions that lead to two different mechanisms of growth: either growth by aggregation and recrystallization of primary particles or direct crystal growth. When growth was dominated by aggregation of primary units, the magnetic field had a dramatic effect on the morphology, inducing the formation of rodlike particles. Growth dynamics of that system were studied for particles obtained in the presence as well as in the absence of the magnetic field. Particles were also characterized by powder magnetometry, electrophoresis, X-ray diffraction, and optical absorbance techniques. Interestingly, growth dynamics of the rods cross section were comparable to those of the diameter of the spheres. With the exception of the morphology, no other significant difference was found between the rodlike particles and the spheres.