Magnetisation: The process of generating magnetic properties

Magnetisation describes the process by which a material takes on magnetic properties, either through an external magnetic field or through electric currents. It is a central property of magnetism and plays a key role in electrical engineering, materials science and physics. Magnetisation is often denoted by the symbol ( M ) and is measured in units of amperes per metre (A/m).

How does magnetisation work?

Magnetisation of a material occurs by aligning the magnetic moments of atoms or molecules in a preferred direction. This process can take place in two ways:

• Through an external magnetic field: An external magnetic field causes the magnetic moments of the atoms or molecules to align themselves along the field.
• Through electric currents: If current flows through a coil or conductor, the material inside is magnetised by the magnetic field generated.

Types of magnetisation

• Ferromagnetic magnetisation: Ferromagnetic materials such as iron retain their magnetisation even after the external field has been removed. This is the basis for permanent magnets.
• Paramagnetic magnetisation: In paramagnetic materials, the magnetic moments are weak and disappear as soon as the external field is removed.
• Diamagnetic magnetisation: Diamagnetic materials generate a weak magnetic field that is opposite to the external field and are easily repelled.

Properties of magnetisation

• Material dependence: The strength of the magnetisation depends on the properties of the material, such as the permeability and the arrangement of the magnetic moments.
• Maximum magnetisation: Saturation magnetisation occurs when all magnetic moments are fully aligned and no further magnetisation is possible.
• Reversibility: With soft magnetic materials, magnetisation is reversible, while with hard magnetic materials it can be permanent.

Formula of magnetisation

Magnetisation ( M ) is defined as the magnetic moment per unit volume:

M = m / V

Where:

• ( M ): Magnetisation (in A/m)
• ( m ): Magnetic moment (in ampere-square metres, A-m²)
• ( V ): Volume of the material (in cubic metres, m³)

Applications of magnetisation

Magnetisation is a fundamental process in many technical and scientific applications:

• Permanent magnets: The production of permanent magnets is based on the magnetisation of ferromagnetic materials.
• Electric motors and generators: Magnetised materials generate the magnetic fields required to convert energy.
• Magnetic data storage: Hard drives store information by selectively magnetising small areas.
• Transformers: Magnetisation is used to efficiently transfer electrical energy between coils.

Interesting facts about magnetisation

Did you know that magnetisation also occurs in nature? Rocks such as magnetite are magnetised by the Earth's magnetic field, creating natural magnets. These so-called "lodestones" were the first magnets discovered by humans and led to the invention of the compass.