Ferromagnetism: The strongest form of magnetism

Ferromagnetism is a physical property of certain materials that can exhibit particularly strong magnetisation. It describes the phenomenon in which the magnetic moments of the atoms or molecules in a material are aligned in parallel, creating a strong, permanent magnetic field. Ferromagnetism is the basis for many applications in technology and industry.

How does ferromagnetism work?

Ferromagnetic materials contain atoms with unpaired electrons whose magnetic moments are aligned parallel to each other through the so-called exchange interaction. This interaction strengthens the magnetic moment and leads to strong magnetisation. The behaviour is explained by so-called magnetic domains, small areas in the material in which all moments are uniformly aligned.

If an external magnetic field is applied, the domains in the material align themselves along the field. After the field is removed, the alignment remains in many materials, creating a permanent magnet.

Properties of ferromagnetism

• Hysteresis: Ferromagnetic materials exhibit a characteristic hysteresis effect in which the magnetisation does not disappear immediately when the external field is removed.
• Curie temperature: Above this temperature, ferromagnetic materials lose their magnetic properties as the thermal movement disturbs the alignment of the moments.
• High magnetisation: Ferromagnetic materials can be strongly magnetised and generate a permanent magnetic field.

Examples of ferromagnetic materials

• Iron (Fe): The most common ferromagnetic material used in numerous industrial applications.
• Nickel (Ni): Used in alloys and for corrosion-resistant applications.
• Cobalt (Co): Known for its high temperature stability and use in high-performance magnets.
• Alloys: Materials such as AlNiCo and neodymium-iron-boron (NdFeB) combine ferromagnetic properties with increased performance.

Typical applications of ferromagnetism

Ferromagnetism plays a central role in many technologies:

• Electric motors: Ferromagnetic cores strengthen the magnetic field and increase efficiency.
• Transformers: In power transmission, ferromagnetic cores minimise energy losses.
• Magnetic data storage: Hard drives and magnetic tapes use ferromagnetic layers to store data.
• Loudspeakers: Permanent magnets made of ferromagnetic materials drive the membranes.

Interesting facts about ferromagnetism

Did you know that the discovery of ferromagnetism played a key role in the development of modern physics? Scientists such as Pierre Curie and Wilhelm Weber contributed significantly to our understanding. Their research laid the foundations for applications ranging from electric motors to data processing.