SOFT FERRITES

Soft ferrites are crystalline oxides whose main constituents are oxygen, iron and one or more of the metallic elements such as Mn, Ni, Mg and Zn. In addition, for the purpose of attaining certain desired properties, the composition may include metallic and non-metallic additives such as Co and Si. The soft ferrites are sometimes called spinel ferrites because they have a crystal structure similar to that of the mineral spinel. These ferrites are ceramics whose mechanical properties like brittleness, hardness, strength, etc. are similar to those of ceramics we use as tiles, kitchenware, furnace linings and electrical insulators. However, ferrites differ from many of these ceramics by having an additional and important properties: Ferrites are magnetic.

Advantage over other magnetic materials

Most other technologically useful magnetic materials such as iron and metallic alloys have low electrical resistivity. This makes them useless for applications at high frequencies, for example as inductor cores in TV circuits. The problem is that their low electrical resistivity allows induced currents (called eddy currents) to flow within the materials themselves, thereby producing heat. This is wasted energy and the heat is often a serious problem. Thus, the materials become inefficient as they waste energy, the more so as the frequency gets higher. However, ferrites can perform much better at high frequencies because they have high electrical resistivity. High permeability and time/temperature stability are important additional characteristics which have widened the use of ferrites into high-frequency and wide- band transformers, quality filter circuits adjustable inductors, delay lines and other high- frequency electronic circuitry. Actually, at high frequencies the use of ferrites is relatively more routine compared to that of other circuit components whose performance continues to need improvement. An important factor in choosing ferrites is that they are generally cheaper than magnetic metals and alloys. Ferrites are the best core material choice for frequencies from 10KHz to a few hundred MHz when one requires the combination of low cost, high Q, high stability and lowest volume. Furthermore, no other magnetic material has magnetic and mechanical parameters as flexible as those of ferrites.

Hence, ferrites have advantages which can be summarised as follows: