• Ferri- and antiferromagnetism
• Field lines

Ferrite

Ferrite magnets are easily recognized by their black color. Most people know them from school, where they are used, for example, as classic blackboard magnets - but they are also used in industry. Their great advantage lies in the fact that they are very robust and temperature resistant.
Ferrite magnets can withstand temperatures of up to 250 °C and are hardly susceptible to aggressive chemicals such as acids or salts.
This is another reason why they are the most produced type of magnet in the world. However, they are particularly popular because they are comparatively cheap to produce. Accordingly, ferrite magnets are often used as cheap permanent magnets in products such as:

• Loudspeakers
• Microphones
• Engines
• Pumps

What is Ferrite?

Ferrite is a so-called ferrimagnetic substance and, together with neodymium, is one of the best-known magnetic materials.

A basic distinction is made between magnetically hard and magnetically soft ferrites. The latter have the lowest possible coercivity, while the former have the highest possible.
Soft-magnetic ferrites are used, for example, in electrical engineering as magnetic cores, chokes, coils or transformers.
Hard ferrite magnets, on the other hand, are used as permanent magnets - for example in loudspeakers.

Depending on the type of manufacture, ferrite magnets are also subdivided into weaker isotropic and stronger anisotropic.

The production of ferrite magnets

The ceramic ferrite magnets are usually manufactured in a sintering process - also called calcination. This is a chemical reaction with the starting materials iron oxide and barium or strontium carbonate.

In the first step, the materials are "pre-sintered" and then ground as finely as possible. Finally, the compacts are formed, then dried and sintered. The raw magnets can be formed in an external magnetic field.
The grains are thus brought into a preferred orientation (anisotropy).

The so-called dry pressing process can also be used for small and geometrically simple shapes for processing workpieces. Poorer magnetic characteristics compared to the parts manufactured using the wet pressing process result from the strong tendency towards (re-)agglomeration of the smallest particles. Although concentrated calcination and sintering can be performed on compacts formed directly from the magnetic materials, the magnetic characteristics of the products thus formed are extremely poor.

The special feature of the wet pressing process lies in the emulsion created from alloy powder and liquid. Filling channels ensure that the emulsion reaches the pressing tool via injection.

The wet pressing process is more complex than the dry pressing process. In the end, however, stronger magnetic properties are also created.

What are the advantages and disadvantages of ferrite magnets?

A big advantage is that ferrite magnets have a high coercivity and high specific resistance. The latter makes their use in changing magnetic fields possible. In addition to their low price, they are also valued for not being susceptible to corrosion. A special superficial treatment is therefore not necessary. Finally, they are characterized by their special resistance to high temperatures: Their ability to be used at operating temperatures of - 40 °C to + 250 °C makes them real all-round helpers.

However, ferrite magnets are not as powerful as, for example, neodymium magnets and samarium-cobalt magnets. This is due to their comparatively low magnet strength and low demagnetization resistance.
It should also be considered: Ferrite magnets are characterized by two different mixtures - SrFe and BaFe - i.e., strontium ferrite and barium ferrite. Although BaFe is generally less expensive than SrFe, it is less efficient than SrFe. A major advantage of SrFe is that it is approved for use with drinking water. In contrast, the possible uses of BaFe with barium in this area of application are problematic, which is why only SrFe ferrite magnets are often offered.

What types of ferrite magnets are there?

• Ferrite ringmagnets
• Ferrite blockmagnets
• Ferrite cubemagnets
• Ferrite discmagnets

Depending on the application, different sizes, thicknesses and diameters are available. Especially small magnets are often used in private spaces as holding or fridge magnets. The models are also ideal as magnetic toys for children.

Ferrite magnets vs neodymium - which is better?

There is no general answer to the question of whether neodymium or ferrite magnets are better.
Basically, neodymium magnets have by far the greatest adhesive force, which is why they are sometimes referred to as super magnets. That is why they are increasingly used, for example, in the construction industry or in the real estate sector. A disadvantage, however, is that they are not very resistant to corrosion. Therefore, they are often reinforced with a protective additional coating.
Ferrite magnets are not as strong as neodymium magnets but are very heat and corrosion resistant.
Very different areas of application open for the two types of magnets.

Magnetic characteristics of ferrite magnets

In our shop, we indicate the Chinese standard, such as Y30 or Y35, as the degree of magnetization of ferrite magnets. The corresponding classification of the American classes (C8, C11) can be found in the following table:

Technical specifications of hard ferrite magnets according to DIN IEC 60404-1-1: