The largest volume of industrial permanent magnet materials is of the ferromagnetic oxides, one of which is magnetic cera; lie material known as Hard Ferrite. This material is distinguished by its high coercivity, which is an important parameter which indicates the material's magnetic hardness, and exceeds the value of 12.5 Oe, (IkA/m). Soft magnetic materials, such as Soft Ferrites, for example have coercivities of only a few (A/m) - Oe. The high coercivity such as (250 A/m) - 4000 Oe permits magnets of short magnetic lengths, to be used without excessive self demagnetisation. The high electrical resistivity, of the order of lO^Qm minimizes eddy current losses and thus makes Hard Ferrite an ideal material for high frequency applications.
Low permeability, 1 to 2, of the material helps one to generate multi-poles on the surface of magnetic body. Even complicated magnetic patterns can be formed with ease.
Hard Ferrite is a ceramic material which is hard and brittle and close dimensional tolerances can only be achieved by grinding.