Can a Magnet Lose its Properties?

Everyone knows what a magnet is, but not all understand magnetic properties and how they are affected by time, temperature, wear and external magnetic fields. Magnets are made from ferromagnetic materials and have tiny magnetic domains. In the natural state, these domains aren't aligned and exhibit little if any magnetism. When a strong magnetic field is applied, it forces alignment and the material becomes magnetic

Types of Magnet

Magnets can be permanent, retaining their magnetic alignment after magnetism, or temporary, such as electro magnets that lose their magnetism when the magnetic field is removed. Various materials exhibit magnetic properties including:

• Iron:Used for electro magnets as well as in a permanent magnet

• Iron oxides:Haematite, magnetite and ferric oxide.

• Nickel:Magnetic to moderate temperatures

• Cobalt:Retains magnetism at high temperatures

• Alloys:Certain alloys of iron, nickel or cobalt

• Rare earth:Samarium and Neodymium magnets

Permanent Magnet

Permanent magnets are commonly manufactured from a combination of materials. Common types include:

• Ferrite:Known as a ceramic magnet and made from strontium ferrite, cheap and corrosion-resistant but brittle and hard to machine. Usable to 250 °C.

• Alnico:Alloy of aluminium, nickel, iron and cobalt with good corrosion resistance and practical to 425 °C.

• Neodymium:Powerful neodymium magnets made from neodymium, iron and boron, often plated or epoxy encased to improve corrosion resistance and limited to 200 °C.

• Samarium:Made from cobalt and samarium, expensive, powerful, corrosion-resistant and withstand temperatures to 350 °C.

• Plastic:A powdered permanent magnet bonded with thermoplastics. Excellent mechanical properties but limited to 120 °C.

• Magnet Wear A magnet can wear out and this needs to be considered.

Factors that cause loss of magnetic properties include:

• Erosion:Magnetic strength is directly dependent on physical dimensions, so wear and tear as well as pieces broken off lead to less magnetic force. A ferrite magnet is particularly vulnerable to chipping.

• Corrosion:Disrupts the physical structure by forcing magnetic domains apart and encouraging them to lose orientation.

• Elevated temperature:Magnetic materials lose magnetism as they heat, but they regain magnetism when cooled provided the maximum temperature is below their Curie temperature. Above the Curie temperature, a magnet permanently loses all or some of its magnetism.

• External magnetic fields:Strong, opposing magnetic fields can cause the magnetic domains to lose their orientation and relax into a lower state of energy where they are not aligned. This tendency can be reduced by adding materials that help constrain magnetic domains in the right orientation.

• Time:Although a magnet becomes weaker over time, the rate of natural demagnetism depends on operating temperature and external magnetic fields and takes many years provided the magnet is kept below its maximum operating temperature.

• Choosing the Right MagnetThere are many factors that go into choosing the best magnet for each application. These include cost, required magnetic force, resistance to corrosion, shape and operating temperature. If you are facing a challenge finding the right magnet for your application, send us the details of what you need and let us recommend the best magnet for your application.