FAQ - Frequently Asked Questions (and their answers!)

What is the difference between the combination magnet-magnet and magnet-iron?

Magnets and iron attract each other, but are hardly able to repel each other.

At full contact, the attraction between magnet and iron is the same as between two equal magnets. As the distance increases, however, the attraction between magnet and iron becomes distinctly weaker than the attraction between two equal magnets. This is due to the iron's low remanence.

Difference regarding repulsion

A permanent magnet and in iron plate attract each other, but there is no repulsion, like you can find between two permanent magnets (see FAQ regarding attraction and repulsion).

Difference regarding attraction

At full contact, the attractive force between a permanent magnet and an iron plate is the same as the attractive force between two permanent magnets. However, the attraction diminishes with increasing distance quicker than the attraction between two permanent magnets (see graph).

x axis: distance
y axis: adhesive force

pink: attraction magnet-magnet
blue: attraction magnet-iron

example: disc magnet S-12-06-N

left: ferromagnetic material
right: molecular magnet

Explaining the phenomenon

Ferromagnetic material (iron, cobalt, nickel) contains microscopically small permanent magnets (molecular magnets). These molecular magnets rotate individually and can be adjusted by external magnetic fields. The material is thereby magnetised.

Explaining remanence

Also a super magnet contains molecular magnets. During the production of a permanent magnet, they are adjusted by a very high field that is produced by electromagnets. After turning off this external magnetic field, the alignment in the permanent magnet stays more or less intact (remanence: remanere = remain). A permanent magnet can now, in turn, adjust and thereby magnetise the molecular magnets in other ferromagnetic material. That's what happens at full contact between magnet and iron: The magnet transfers its magnetisation to the iron and the iron acts like a magnet.

left: permanent magnet
right: ferromagnetic material

Difference regarding remanence

The alignment of the molecular magnets does not stay permanent in every ferromagnetic material. After removing the external magnetic field, a lot, a little or practically no magnetisation may remain, depending on the internal features of the material.

In a piece of high-purity iron, for instance, the order of molecular magnets disintegrates completely after removing the external field. In a normal iron plate the alignment stays intact a little better, but it is still a lot less than in a super magnet.

Practical implication

The attraction between a permanent magnet and a steel plate diminishes quickly with increasing distance, because the magnetisation in the steel plate decreases quickly. Two permanent magnets attract each other more with increasing distance, because the magnetisation in both magnets remains practically the same.