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Magnetic properties of matter

Magnetism is caused by the movement of charged particles.

All matter contains electrons that orbit the nuclei of atoms at high speeds. Each of these electrons creates a tiny magnetic field due to its motion.

A domain is a small region in which these magnetic fields are aligned. In most materials, the domains are arranged randomly and they cancel each other out.

However, in magnets the domains are aligned so that they add up instead of cancelling each other out.

In all magnetic materials, the domains can be forced to align, making a new magnet!

In non-magnetic materials, the domains cannot be aligned.

Organisation of domains (individual magnetic fields) within a normal material and a magnet.
Organisation of domains (individual magnetic fields) within a normal material and a magnet.

Magnetisation is the process of converting a magnetic material into a magnet.

To magnetise an object made out of magnetic material, the magnetic regions (domains) inside the material are forced into an arrangement where their magnetic fields add up.

An iron bar can be turned into a magnet by forcing the domains inside the bar to align.

Non-magnetic materials cannot be magnetised. The domains can never be arranged to give an overall magnetic field.

Copper cannot be magnetised because it is not a magnetic material.

When a magnet is demagnetised, its domains are randomised so that the overall magnetic field is removed. This is the opposite of magnetisation.

Magnetic effects in an unmagnetised (above) and magnetised (below) magnetic material
Magnetic effects in an unmagnetised (above) and magnetised (below) magnetic material

Magnetic materials can be classified depending on how easily they can be magnetised and how long the magnetisation lasts:

  • A soft magnetic material is magnetised easily but loses its magnetism very quickly.

    This is because the magnetic regions (domains) inside soft materials can be aligned very easily.

    Iron is a soft magnetic material.

    Soft magnetic materials are used to make temporary magnets.

  • A hard magnetic material is difficult to magnetise but remains magnetised for longer periods.

    This is because the magnetic regions (domains) inside hard materials do not align very easily.

    Steel is a hard magnetic material.

    Hard magnetic materials are used to make permanent magnets.

    Bar magnets and fridge magnets are permanent magnets.

Fridge magnets are permanent magnets. They stay stuck to the fridge for long periods of time.
Fridge magnets are permanent magnets. They stay stuck to the fridge for long periods of time.

Magnetic induction is the temporary magnetisation of a magnetic material due to an external magnetic field.

The end of the magnetic material that is near the north pole of the magnet becomes a south pole and the other end becomes a north pole .

The induced magnet loses its magnetism once the magnet is removed. A soft magnetic material will lose its magnetism more quickly than a hard material. Magnetic induction creates a temporary magnet.

When an iron nail is brought near a magnet, it becomes an induced magnet.

The iron nail is able to attract other magnets and magnetic materials. Once the magnet is pulled away from the nail, the nail quickly loses its magnetism.

The north pole of the magnet induces a south pole in the head of the nail. The nail is subsequently attracted to the magnet.
The north pole of the magnet induces a south pole in the head of the nail. The nail is subsequently attracted to the magnet.