Why do magnets lose their strength?
Short answer: a neodymium magnet loses virtually no strength by itself, not even through use: at normal temperature less than 1% in 10 years. It only gets weaker through (1) too much heat, above approx. 80 °C, (2) rust after the coating has been damaged, (3) breakage or chipping, or (4) a strong opposing magnetic field. If a magnet seems weaker, it is usually due to the surface or a small distance.
Causes of loss of strength at a glance
| Cause | Permanent? | How to prevent it |
|---|---|---|
| Heat above the max. operating temperature (N: 80 °C) | Yes, partly | Choose an H/SH grade or a thicker magnet; see magnets at high temperatures |
| Heat below the max. operating temperature | No, returns after cooling | Nothing needed |
| Rust after damaged coating | Yes, the material crumbles | Do not let them snap together; outdoors use epoxy, plastic or rubber; see why do neodymium magnets rust? |
| Breakage, chips, broken edge | Yes, less volume | Do not let magnets slam together; use a dispenser |
| Strong opposing field (another large magnet, electromagnet) | Yes, partly | Do not force magnets together with like poles at high temperature |
| Ageing | Negligible (< 1% in 10 years) | Nothing needed |
Does a magnet lose strength through use?
No. A permanent magnet does not supply energy when it holds something, just as a table does not use energy when a book lies on it. You can remove and replace a magnet thousands of times without it getting weaker. Only the coating can be damaged by repeated snapping.
Does your magnet seem weaker? Check this first
- Is there paint, lacquer, film, glue or dirt between the magnet and the steel? Every 0.5 mm counts.
- Is the steel thinner or different than before, or is it stainless steel?
- Is the load now sideways instead of perpendicular?
- Is a piece missing from the magnet, or is there rust under the coating?
More about these factors in how is holding force determined?
Can you remagnetise a magnet?
Yes, but only with a magnetiser (a coil with a very strong current pulse, often more than 3 Tesla). It does not work with another magnet. For loose small magnets, replacing is almost always cheaper. A magnet that has been above the Curie point or is affected by rust will not fully recover.
Frequently asked questions
How long does a neodymium magnet last?
With normal indoor use, decades. The limiting factor is usually the coating, not the magnetism.
Can a magnet make another magnet weaker?
Hardly at room temperature, because neodymium has a high coercivity. At higher temperatures or with a much stronger magnet it can. See what is coercivity?
Does a magnet get weaker if it is dropped?
The magnetism does not, but neodymium is brittle. A fall onto stone can cause a chip or crack, leaving less magnet.
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