Ferrite magnets were first reported in the 1930’s, went into large-scale production in the 1950’s, and are now the largest selling magnet type. Changes in prefiring time and temperature, along with changes in the sintering temperature, and chemical additives such as Cobalt or Lanthanum can be used to enable a wide range of magnetic properties. 

Ferrite magnets are produced by calcining a mixture of iron oxide and strontium carbonate to form a metal-oxide ceramic, SrO•6(Fe2O3).  The carbonate and rust are mixed then loaded into a high-temperature reactor that drives off CO2. The resulting compound is milled to ~1 µm then sieved. That material is usually mixed with water and pumped into large presses as a mud. After the die cavities are filled an electromagnetic field is applied to set the direction of anisotropy. Post pressing, the wet compacts are removed from the die cavities and sintered in open air. 

These magnet materials are unique in a number of ways:

• They are electrically nonconductive. This allows them to witness large fluctuations in the magnetic field (such as in a motor) without producing eddy currents that will cause heat and losses. 

• Ferrite particles are platelets with the preferred direction of magnetization normal to the C-axis. This allows for the production of some anisotropic materials using only mechanical alignment.

• Press dies can have 1 to >64 cavities. Tooling is large, complex, & can be expensive. 

• The reversible temperature coefficient of B is 2-10 times that of other magnet materials; -0.2%/C

• The reversible temperature coefficient of Hcj is +0.4 %/C. It gains coercivity as it gets hotter and is subject to demagnetization when cold.

Data Sheet