Soft Magnetic Ferrites 101


The single most import characteristic of soft ferrites, as compared to other magnetic materials, is the high volume of resistivity exhibited in the monolithic form. Since eddy current losses are inversely proportional to resistivity and these losses increase with the square of the frequency, high resistivity becomes an essential factor in magnetic materials intended for high frequency operation. The magnetic properties of ferrite components are isotropic, and by employing various pressing, injection molding, and/or grinding techniques, a wide range of complex shapes can be formed. There is no other class of magnetic material that can match soft ferrites in performance, cost and volumetric efficiency, from audio frequencies into the GHz range.

During the last 50 years the basic constituents of ferrites have changed little, but purity of raw materials and process control have improved dramatically. Ferrites are ceramic materials with the general chemical formula MO. Fe3O3, where MO is one or more divalent metal oxides blended with 48 to 60 mole percent
of iron oxide. Fair-Rite manufactures three broad groups of soft ferrite materials:

Manganese zinc
(Fair-Rite 31, 73, 75, 76, 77, 78, 79, 80, 97, 95 and 98 materials)

Nickel zinc
(Fair-Rite 15, 20, 43, 44, 51, 52, 61, 67, 68 and 80 materials)

Magnesium zinc (Fair-Rite 46 Material)

Manganese zinc (MnZn) ferrites are completely vitrified and have very low porosity. They have the highest permeabilities and exhibit volume resistivities ranging from one hundred to several thousand ohmcentimer. Manganese zinc ferrite components are used in tuned circuits and magnetic power designs from the low kilohertz range into the broadcast spectrum. These ferrites have a linear expansion coefficient of approximately 10 ppm/°C.

The nickel zinc (NiZn) ferrites vary in porosity, and frequently contain oxides of other metals, such as those of magnesium, manganese, copper and cobalt. Volume resistivities range from several kilohm­centimeter to tens of megohm-centimeter. In general, they are used at high frequencies (above 1 MHz), and are suitable for low flux density applications. Nickel zinc ferrites have a linear expansion coefficient of approximately 8ppm/°C.

The magnesium zinc (MgZn) ferrite has similar characteristics as NiZn ferrite. The composition of MgZn material does not contain any nickel, hence avoiding potential environmental issues as well as reducing the raw material component cost.

As is evident from the flow diagram on page (TBD) there is considerable processing involved, and the manufacturing cycle will take a minimum of two weeks. The parts listed in the catalog represent a broad cross section of the wide variety of cores produced by Fair-Rite Products. Large OEM quantities are manufactured by Fair-Rite to order. Most of the more commonly used parts are stocked by our distributors, offering prompt deliveries. For a complete listing of our distributors visit our website

Many of the parts produced by Fair-Rite are made to customer specifications, and we welcome inquiries involving application specific designs. We have the capabilities to design tooling rapidly and have it fabricated either by our own tool shop or by outside vendors.