The Use of Precipitated Ferrite Powders for Anisotropic Sintered Magnets

摘要

Ferrite magnets are usually produced with powders obtained by the calcination of iron oxides and barium or strontium carbonates mixtures (ceramic method). These powders are milled to obtain monocrystalline (single domain) particles, which can be aligned just before compaction, to get an anisotropic product with improved magnetic properties. On the other hand, co-precipitation is an alternative process that can produce very fine particles with high purity, and intrinsic magnetic properties, as coercivity, better than those of ceramic powders. The use of ferrite powders obtained by co-precipitation to produce anisotropic sintered magnets is investigated here. Iron and barium chlorides were used as raw materials. The Fe/Ba molar ratio, pH, and calcination temperature were adjusted to get higher magnetic performance. The powders were aligned in a magnetic field, pressed and sintered. Magnetic properties, especially the ratio between remanence and maximum specific magnetization, and also microstructure were evaluated.