Magnetically hard: Materials with high magnetisation stability

The term magnetically hard describes materials that are highly resistant to demagnetisation. They are difficult to magnetise, but retain their magnetisation very stably, even when exposed to opposing magnetic fields. Magnetically hard materials are often used to produce permanent magnets, which have a permanent magnetic effect.

Properties of magnetically hard materials

• High coercivity: Magnetically hard materials require a strong opposing magnetic field in order to be demagnetised.
• Stable magnetisation: Once magnetised, they retain their magnetisation over long periods of time.
• High hysteresis loop: The hysteresis curve of magnetically hard materials is broad, which indicates a high stability of the magnetic domains.
• Mechanical robustness: Many magnetically hard materials, such as neodymium-iron-boron, are also mechanically resistant.

Examples of magnetically hard materials

• Neodymium-iron-boron (NdFeB): Extremely strong magnets with high coercivity, used in electric motors and loudspeakers.
• Samarium-Cobalt (SmCo): High-performance magnets that remain stable even at high temperatures.
• Ferrite magnets: Cost-effective magnets that offer moderate hardness and durability.

Comparison: Magnetically hard vs. magnetically soft

Magnetically hard and magnetically soft materials differ fundamentally in their magnetisation and use:

• Magnetically hard: Difficult to magnetise, but retain their magnetisation permanently. Ideal for permanent magnets.
• Magnetically soft: Easy to magnetise, lose their magnetisation quickly. Suitable for electromagnetic applications such as transformers.

Applications of magnetically hard materials

Materials that are magnetically hard are used in numerous technologies:

• Permanent magnets: In electric motors, generators and hard drives.
• Medical technology: In MRI machines and implants where stable magnetisation is required.
• Sensor technology: Magnetic field sensors and switches that rely on permanent magnetic fields.
• Household: Fridge magnets, magnetic holders and door locks.

Interesting facts about magnetically hard materials

Did you know that neodymium magnets, which are among the magnetically hardest materials, can develop a magnetic force that can lift thousands of times their own weight? Despite their strength, they are susceptible to corrosion and are therefore often coated with layers such as nickel or epoxy resin to increase their lifespan.