Ceramic magnets became commercially available in the 1950’s (Alnico magnets were the first true magnets to be introduced n the 1930’s). They are called Ceramic magnets because of their electrically insulating properties and their production method. They are better known as Ferrite Permanent Magnets but their correct title should be hard hexagonal ferrite permanent magnets. There are currently 27 grades of Ferrite Permanent Magnet available.
Ferrite magnets have ferrimagnetic properties. Compared to Alnico, it has much higher Intrinsic coercivity making it much better at resisting demagnetisation from external magnetic fields and from other magnets). This allowed it to be used much more successfully in electric motors and generators where it is still an extremely popular magnet. The hexagonal ferrite structure is found in both BaO.6Fe2O3 and SrO.6Fe2O3 (the chemical symbols for each type of ferrite), but Strontium (Sr) version of ceramic ferrite magnet has stronger magnetic properties.
Ceramic ferrite magnets are often extremely low cost, due to the ease of processing and the low cost of raw materials. As a result they are one of the most widely used permanent magnet materials in the world.
The magnets are made by a powder metallurgy processing route and there are no problems with oxidation of the powder during processing, as the material is already a stable oxide. The powder processing route ensures that the magnets comprise of very small grains (<1mm), which is essential for generating coercivity in these magnets. During processing the powder is compacted in a magnetic field in order to align the easy direction of magnetisation of the particles and hence enhances the remanence and the maximum energy product.
Please be aware the material discussed here is ferrite permanent magnets - they are not the same as ferrite cores as used in transformers. Ferrite magnets retain their magnetism; transformer ferrites (e.g. C-cores, E-cores, ring cores, etc) only have magnetism when an electrical current passes through the surrounding coil which disappears when the current is turned off - they work in completely different ways. Ferrite magnets are called hard ferrite magnets - high Hc and Hci values; Transformer ferrites are soft ferrites - much lower Hc and Hci values.
Ferrite magnets can be produced in many shapes and sizes. The main shapes are blocks, discs, rings, arcs, and rods. Other shapes may be possible upon request. The list of available magnet grades is as follows (Y30 and Y30H-1 are the most popular):-
Y8T - Br=2.0~2.35, Hc=1.57~2.01kOe, Hci=2.64~3.52kOe, BHmax=0.8~1.2MGOe.
Y10T - Br=2.0~2.35, Hc=1.61~2.01kOe, Hci=2.64~3.52kOe, BHmax=0.8~1.2MGOe.
Y20 - Br=3.2~3.8, Hc=1.70~2.39kOe, Hci=1.76~2.45kOe, BHmax=2.3~2.8MGOe.
Y22H - Br=3.1~3.6, Hc=2.76~3.14kOe, Hci=3.52~4.02kOe, BHmax=2.5~3.0MGOe.
Y23 - Br=3.2~3.7, Hc=2.14~2.39kOe, Hci=2.39~2.89kOe, BHmax=2.5~3.2MGOe.
Y25 - Br=3.6~4.0, Hc=1.70~2.14kOe, Hci=1.76~2.51kOe, BHmax=2.8~3.5MGOe.
Y26H - Br=3.6~3.9, Hc=2.76~3.14kOe, Hci=2.83~3.20kOe, BHmax=2.9~3.5MGOe.
Y26H-1 - Br=3.6~3.9, Hc=2.51~3.14kOe, Hci=2.83~3.20kOe, BHmax=2.9~3.5MGOe.
Y26H-2 - Br=3.6~3.8, Hc=3.30~3.62kOe, Hci=4.00~4.40kOe, BHmax=3.0~3.5MGOe.
Y27H - Br=3.7~4.0, Hc=2.58~3.14kOe, Hci=2.64~3.20kOe, BHmax=3.1~3.6MGOe.
Y28 - Br=3.7~4.0, Hc=2.20~2.64kOe, Hci=2.26~2.76kOe, BHmax=3.3~3.8MGOe.
Y28H-1 - Br=3.8~4.0, Hc=3.02~3.27kOe, Hci=3.14~3.52kOe, BHmax=3.4~3.8MGOe.
Y28H-2 - Br=3.3~3.8, Hc=3.41~3.71kOe, Hci=4.80~5.09kOe, BHmax=3.3~3.8MGOe.
Y30 - Br=3.7~4.0, Hc=2.20~2.64kOe, Hci=2.26~2.76kOe, BHmax=3.3~3.8MGOe.
Y30BH - Br=3.8~3.9, Hc=2.80~2.95kOe, Hci=2.90~3.08kOe, BHmax=3.4~3.8MGOe.
Y30H-1 - Br=3.8~4.0, Hc=2.89~3.46kOe, Hci=2.95~3.64kOe, BHmax=3.4~4.0MGOe.
Y30H-2 - Br=3.95~4.15, Hc=3.46~3.77kOe, Hci=3.90~4.21kOe, BHmax=3.4~4.1MGOe.
Y32 - Br=4.0~4.2, Hc=2.01~2.39kOe, Hci=2.07~2.45kOe, BHmax=3.8~4.2MGOe.
Y32H-1 - Br=4.0~4.2, Hc=2.39~2.89kOe, Hci=2.89~3.14kOe, BHmax=4.0~4.4MGOe.
Y32H-2 - Br=4.0~4.4, Hc=2.81~3.02kOe, Hci=2.89~3.14kOe, BHmax=3.9~4.3MGOe.
Y33 - Br=4.1~4.3, Hc=2.76~3.14kOe, Hci=2.83~3.20kOe, BHmax=4.0~4.4MGOe.
Y33H - Br=4.1~4.3, Hc=3.14~3.39kOe, Hci=3.14~3.46kOe, BHmax=4.0~4.4MGOe.
Y34 - Br=4.2~4.4, Hc=2.51~2.89kOe, Hci=2.58~2.95kOe, BHmax=4.1~4.5MGOe.
Y35 - Br=4.3~4.5, Hc=2.70~3.00kOe, Hci=2.73~3.03kOe, BHmax=4.2~4.8MGOe.
Y36 - Br=4.3~4.5, Hc=3.10~3.41kOe, Hci=3.14~3.44kOe, BHmax=4.4~4.8MGOe.
Y38 - Br=4.4~4.6, Hc=3.58~3.83kOe, Hci=3.69~3.90kOe, BHmax=4.6~5.1MGOe.
Y40 - Br=4.4~4.6, Hc=4.15~4.45kOe, Hci=4.27~4.52kOe, BHmax=4.7~5.3MGOe.