Ionic exchange effects and magnetic properties of nanocrystalline BaFe/sub 12/O/sub 19/ ferite dispersions

Magnetic oxide powders suspended in a liquid spontaneously agglomerate unless they are suitably deflocculated by creating mutually repelling charged double layers or by physically preventing the close approach of particles due to the steric hindrance of absorbed molecules. For hexagonal barium ferrite powder the problem of particles separation is extremely difficult. In processing of materials for magnetic recording, several different additives must be incorporated in the final product to establish the behavior and properties required for the coating. These additives may be categorized conveniently as follows: 1) liquid / solvent medium, 2) surfactant (wetting agent), 3) deflocculant and 4) binder / plasticizer and/or pigment. Although most of these substances are added in a relatively small amount and some may be eliminated or do not appear in the final product, from a manufacturing perspective they are essential. The selection and control of these substances are often the key to successful processing or the development of an improved process. The proper selection is based on chemical characteristics and functions of the additive and empirical experience. For all possible applications of Ba-ferrite particles in magnetic recording, the formation of particle stacks must be prevented. Up to now some experiments that attempt to control agglomeration and surfactant screening for -0.1 μm particles in organic solvents have been reported. A variety of ionic and nonionic surfactants were checked for their ability to provide wetting and particle separation. However, all surfactants used, while offering good particle wetting, failed to deliver relatively stable suspension.