Ferrite magnets are brown ferromagnetic ceramics obtained by sintering iron oxide at high pressure and high temperature (>1000°C). Their density is 4.8. This is the family of magnets with the best energy/cost ratio. Their remanent induction is low but the coercive field remains high.Read description
It is a very hard material, which can therefore be machined with a diamond wheel, and is particularly fragile. Its colour is between dark grey and black.
Hard ferrites are strong coercive field magnets, making them more difficult to demagnetise than an alnico magnet. However, we are far from the magnetic properties of an earth-rare magnet (samarium-cobalt or neodymium iron-boron)
Its density is given for a range from 4.75 g/cm3 to 4.90 g/cm3 and its Curie temperature (temperature at which the magnet will be irreversibly demagnetised) is about 450°C. Ferrites have excellent corrosion resistance.
Like Alnico, ferrites can be isotropic or anisotropic.
Ferrites are magnets that have historically been produced in very large quantities on huge production lines; their preferred market is therefore logically the automotive industry. Indeed, they are widely used in electric motors, for example in windscreen wipers. Hard ferrites are also used in a large number of industrial applications for the manufacture of motors, where power is an important parameter to take into account.
- Magnetic force is optimal when the magnet is in contact with a mild steel frame, flat, clean and rather thick. It is lower with allied steels and cast iron (less 30% for cast iron).
- It is lower in presence of an air gap (space between the part to magnetize and the polar face of the magnet).
- It is decreasing by 0.4% every degree C (see besides curve).
INDUCTION ON SURFACE
- The maximum value of induction in surface at 20°C is about 1500 Gauss for Ferrite flat pot magnets and blocks.
- This value is decreasing by 0.2% every degree C, when temperature is increasing.
- These ceramics are very fragile and offer little resistance to shocks.
- They must be handled carefully.
- To avoid magnets attraction during handling we advise to put them on a mild steel plate.
- Do not shock or squeeze.
RESISTANCE TO CHEMICALS
- Ferrite magnets are rustproof
RESISTANCE TO TEMPERATURE
- Induction losses are reversible so far we stay in the limit of working temperature of the material.