Everything about magnets and magnetism from MagnetMax the magnet specialist

Permanent magnets

The elementary magnets of a ferromagnetic material are aligned through magnetisation (see hysteresis) in an external magnetic field. The use of hard magnetic materials ensures that the materials retain their magnetisation even after the magnetic field is switched off and without an electric current at temperatures below the maximum operating temperature. The result is a permanent magnet.
Permanent magnets or permanent magnets consist of  e.g. iron, cobalt and nickel, or alloys thereof.

Hysteresis of magnets

If an external magnetic field is applied to a (not yet magnetised) ferromagnetic material and the resulting magnetisation is measured as a function of the external magnetic field, no linear relationship is observed; rather, the magnetisation saturates from a certain external magnetic field. If the external magnetic field is then reduced to 0 again, a certain residual magnetisation, the so-called remanence, remains. The ferromagnetic material has been magnetised. To reduce the residual magnetisation to zero, a field opposite to the original external magnetic field is required. The field strength at which the magnetisation in the material is reduced to zero is called the coercive field strength. The hysteresis curve describes  the course of the magnetisation in the material as a function of the external magnetic field.
Characteristic points of the hysteresis curve are the saturation magnetisation, the remanence magnetisation and the coercive field strength.
The higher the remanence and coercivity, the stronger the magnet.

Temperature resistance of magnets

An important parameter in relation to the temperature dependence of the magnetism of permanent magnets is the so-called Curie temperature (named after Pierre Curie). The Curie temperature is the temperature at which a ferromagnet changes from a ferromagnetic to a paramagnetic state. This phase transition is reversible. Above the Curie temperature, ferromagnetism no longer occurs; the material is then paramagnetic. If the temperature is lowered back below the Curie temperature, the material becomes ferromagnetic again, but any magnetisation that was originally present is then no longer present. The material must therefore be re-magnetised,
so it is clear that materials can only be used as magnetic materials below the Curie temperature.
In practice, it is important to know that a permanent magnet loses its magnetic polarisation well below the Curie temperature and that this is irreversible.
This (max) temperature is different for different ferromagnetic materials and is a specified property of the respective magnet.

Making magnets

The production of ferromagnets is described here.
Strong permanent magnets are produced using a pressing process. For this purpose, the prepared finely ground base material (e.g. an alloy of rare earths) is pressed into a mould and then sintered at high temperatures. After the sintering process, magnetisation is achieved by a strong external magnetic field and the magnets are brought into the desired final geometry by cutting, sawing and drilling.
Finally, the magnet, whether ferrite, AlNiCo or neodymium magnet, can be provided with a coating adapted to the application.
As a rule, this coating is metallic, e.g. nickel, gold, copper. Nickel, gold, copper, but it can also be organic.
Neodymium magnets are usually coated to make them more resistant to environmental influences.
The finished magnet then undergoes quality control.

Neodymium magnets - the strongest magnets in the world

Ferrite magnets were the measure of all things for a long time and therefore the strongest permanent magnets available.
It was not until the development of rare earth magnets by General Motors and Sumitomo in 1982 that a new era for magnets was ushered in. So-called neodymium magnets made of neodymium, iron and boron (Nd₂Fe₁₄B) have a crystal structure with high anisotropy and extremely high coercive field strengths. With a maximum magnetic energy density of approx. 500 kJ/m³, they put ferrite magnets (typically around 30 kJ/m³) in the shade. The adhesive force of a neodymium magnet is approx. 10 times greater than that of a ferrite magnet of the same volume. In other words, you need a much larger ferrite magnet to generate the same adhesive force as a neodymium magnet.
This makes neodymium magnets, also known as super magnets, the strongest magnets available in the world today.
A neodymium magnet with an edge length of a few centimetres can achieve an adhesive force of several 100 kg.
However, neodymium magnets are more expensive and less weather-resistant than ferrite magnets. To increase resistance to external influences, neodymium magnets are usually coated (e.g. nickel, gold or copper).
The maximum operating temperature of neodymium magnets should also be noted, which is significantly lower than that of ferrite magnets.
 

Open questions

Of course, not all questions about magnets, magnetism, etc. are covered here. You could fill entire books with them, especially if you are also interested in the exact mathematical and physical description of all magnetic phenomena.
However, if you have any further questions that you cannot find answers to under "Information" on the MagnetMax website, you can of course contact the Magnetmax magnet shop team at any time. Our magnet experts will be happy to help you.