Remanence: The remaining magnetisation of a material

Remanence refers to the magnetic flux density that remains in a material after the external magnetic field has been removed. It is one of the key properties of ferromagnetic materials and describes their ability to retain magnetisation. Remanence is measured in units of Tesla (T) or Gauss.

How does remanence occur?

In ferromagnetic materials, the magnetic domains align themselves under the influence of an external magnetic field. After the field is removed, many domains remain in their aligned position, resulting in a residual magnetisation. This remaining magnetisation is the remanence.

The level of remanence depends on the material composition and the strength of the originally applied magnetic field. Materials with high remanence are particularly suitable for the production of permanent magnets.

Properties of remanence

• Remaining magnetisation: Remanence describes how much magnetisation is retained after the external field has been removed.
• Material dependence: Different materials, such as neodymium or ferrite, have different remanence values.
• Influence of hysteresis: Remanence is a point on the hysteresis curve that shows how strongly a material remains magnetised.

Measuring remanence

The remanence of a material is determined using a hysteresis loop measuring device. A magnetisation cycle is run through in which the magnetic flux density ( B ) is recorded as a function of the magnetic field strength ( H ). The remanence corresponds to the value of ( B ) when ( H = 0 ).

Applications of remanence

The property of remanence is used in many technologies and applications:

• Permanent magnets: Materials with high remanence are ideal for the production of permanent magnets that generate a strong magnetic field without a power source.
• Storage media: Remanence is a key property in magnetic storage devices, such as hard discs or magnetic tapes, as it enables information to be stored.
• Electric motors and generators: Permanent magnets with high remanence ensure efficiency and longevity.
• Sensor technology: In magnetic sensors, remanence is used to recognise positions or movements.

Difference to coercivity

While remanence describes the remaining magnetisation, coercivity measures the strength of the opposite field required to cancel out this magnetisation. Both values are crucial for evaluating the properties of a magnetic material.

Interesting facts about remanence

Did you know that remanence is used in archaeology to reconstruct the orientation of the Earth's magnetic field in past times? Magnetic minerals in rocks and ceramics retain their magnetisation over millions of years. This so-called palaeomagnetism helps scientists to understand the movement of continents and changes in the Earth's magnetic field.