We are often asked how long it takes for a magnet to stop being magnetic? Often the question is specific to the magnet type called neodymium magnet/NdFeB/super magnet. For this type of magnet, the answer is short: magnets are permanent and do not lose their strength over time if stored correctly. If you're unsure how long a neodymium magnet is magnetic, this is the answer you need. But, as always, there are nuances and situations when diving deeper into the subject. We'll try to do that in the following sections.
Different types of magnets and their durability
Here we list the most common types of magnets and explain how long they hold their magnetism and what can cause the magnetism to disappear.
1. Neodymium magnets (NdFeB)
A neodymium magnet is a mixture of several different metals. Throughout the manufacturing process, the neodymium magnet is non-magnetic. Only in the final step are the non-magnetic magnets placed in a machine called a magnetiser. In the magnetiser, a strong magnetic field is created. The electrons in the magnets align themselves according to the strong magnetic field and the magnets are now permanently magnetic. Once the magnets have created their magnetic field, it is close to being as permanent as possible. In practice, you can expect a neodymium magnet to lose about 5% of its strength over 100 years. If the neodymium magnet is stored in a safe place without being affected by other magnetic fields, heat, moisture, cold or anything else, the magnet can lose less than 5% strength over 100 years. In other words, it is mainly external influences that can reduce the strength of a neodymium magnet.
- Lifespan: Retains magnetism for hundreds of years under good conditions.
- Causes of magnetic loss: Sensitive to heat (above 80°C to 220°C, depending on grade), impact and corrosion. Therefore, the neodymium magnet should not be exposed to high heat, moisture or impact from hard objects.
2. Samarium cobalt magnets (SmCo)
Samarium-cobalt magnets are made from the materials samarium and cobalt. They are robust and can withstand higher temperatures than neodymium magnets, but they are not as powerful.
- Lifespan: Can maintain magnetism for centuries under good conditions.
- Causes of magnetic loss: Exposure to temperatures above 250°C-350°C, impact and corrosion. Samarium-cobalt magnets should be treated like neodymium magnets, although they can handle higher temperatures and are less sensitive to moisture.
3. Alnico magnets
Alnico magnets consist of aluminium, nickel and cobalt. Their strength is lower than both neodymium magnets and samarium-cobalt magnets, but they have good temperature resistance.
- Lifespan: c
- Causes of magnetic loss: Primarily demagnetised by external magnetic fields, impact and temperatures above 500 degrees.
4. Ferrite magnets
Ferrite magnets are inexpensive and widely used in everyday applications. Their magnetic strength is low, yet sufficient for many purposes.
- Lifespan: Can maintain magnetism for decades to hundreds of years.
- Causes of magnetic loss: Often affected by impact, high temperatures (above 250°C) and exposure to strong magnetic fields. They are generally robust against corrosion. The strong magnetic field from neodymium magnets can demagnetise ferrite magnets, but otherwise it's mostly impacts from hard objects that you need to watch out for.
5. Electromagnets
An electromagnet is a core of iron or ferrite with a coil of metal wire wound around it. Current is passed through the metal wire and a magnetic field is created. When the current is switched off, the magnetic field disappears. As far as electromagnets are concerned, they are magnetic as long as current is passed through the coil.
- Lifespan: Magnetism is present as long as the electromagnet receives current.
- Causes of magnetic loss: Interruptions in electrical power, coil overheating, electrical faults or structural damage.
6. Iron magnets
Iron magnets become temporarily magnetised when exposed to a different magnetic field. For example, if you put a neodymium magnet on a screwdriver, the entire screwdriver becomes magnetic.
- Lifespan: Temporary magnetism that disappears immediately after the other magnetic field is removed.
- Causes of magnetic loss: Absence of an external magnetic field.