Barium ferrite and strontium ferrite are sintered metal oxides BaO2 or SrO2 combined with Fe2O3.
Raw materials for such magnets are abundant and inexpensive. Hard ferrites are the most used permanent magnet materials worldwide. They are made isotropic or anisotropic.
Isotropic magnets have nearly the same magnetic properties in all directions. They can be magnetised accordingly. Their magnetic energy is low and they are inexpensive.
Anisotropic magnets are compressed in a magnetic field, resulting in one preferred direction of magnetisation. In comparison to isotropic magnets their energy density is about 300% higher. The coercivity is high in relation to the remanence. This means that such magnets must have a large pole area, i.e. circular magnets must have a disc shape and not a rod form.
Hard ferrites have a high temperature coefficient. The remanence decreases by about 0.2% per degree C. They can be used between - 40 and + 200°C. Like ceramic materials, they are mechanically hard and brittle. Being oxides they do not corrode and are neither affected by climatic influences nor by many chemicals, with the exception of some strong acids. Machining is only possible with diamond tools. Hard ferrite magnets are standardised in DIN 17 410. IBS Magnet provides standard magnets as discs, rings and wafers from existing form tools.
These metallic alloys made of iron, aluminium, nickel and cobalt plus some copper and titanium are produced by casting in sand moulds or metal moulds and by vacuum investment casting or sintering.
AlNiCo was discovered over 50 years ago and is the oldest magnetic material still used today. Compared to new magnetic materials, AlNiCo magnets have a low coercivity at a higher remanence. AlNiCo magnets must therefore be long in the direction of magnetisation if they are to be able to resist demagnetisation as open-circuit magnets. That means round magnets stipulate the rod shape. The main advantage of AINi-Co is the very low temperature coefficient of only 0.02% per degree C and the wide temperature range from - 273°C to more than + 400°C. Therefore such magnets are used when a constant magnetic field is required over wide temperature ranges. The required rod shape, i.e. the large gap between the poles, is of advantage when operating reed switches. AINiCo magnets are almost only made anisotropic. Due to the increased cost of cobalt and because of the low coercivity, the use of AINiCo magnets is on the decline.
IBS Magnet offers standard AINiCo 500 magnets cast by precision methods as circular rods, as rectangular wafers and in U-shapes. We also offer special holding magnets with AINiCo.
Plastic bonded magnets are widely used nowadays and will increase in importance. The magnet material is pulverised and mixed with suitable plastics. Calendering, extruding and compression or injection moulding are used in producing the magnets.
With flexible plastics and hard ferrite powders, magnetic sheets and strips are produced with a thickness from 0.5 to 8 mm. Those sheets can be coated with white vinyl foil to be used for labels and other signs.
Of a higher magnetic quality are plastic bonded, flexible magnet panels or magnet tapes, which have passed through a homogenous magnetic field during production. As a result the magnetic particles contained in the plastic are orientated and no preferred direction results (anisotropy).