It’s not uncommon for magnets to lose their strength. Known as demagnetization, it occurs with all permanent magnets. When a permanent magnet becomes demagnetized, it will produce a weaker magnetic field, resulting in a lower Tesla (T) reading. What causes demagnetization exactly?
Heat
One of the main causes of demagnetization is heat. Magnets get their power from atoms that are grouped together and aligned in the same direction. Exposure to heat causes these atoms to shuffle and become misaligned.
All magnets have a maximum temperature to which they can heat up before losing their strength. Known as a Curie temperature, they must stay under this temperature to maintain the strength of their magnetic field. If a magnet heats up beyond its Curie temperature, its atoms will shuffle and become misaligned. Short-term exposure to heat may only cause a temporary loss of magnetic strength, but prolonged or repeated exposure to heat can cause a permanent loss of magnetic strength.
Physical Damage
Magnets can become weaker when physically damaged. As previously mentioned, grouped and aligned atoms — magnetic domains — are responsible for a magnet’s strength. Anything that disrupts these atoms so that they are no longer aligned can cause demagnetization.
Physical damage can knock a magnet’s atoms out of alignment. The greater the misalignment of a magnet’s atoms, the weaker its magnetic field will be. Some types of magnets are more susceptible to physical damage than others. Brittle magnets, for instance, are particularly prone to weakening when damaged. Regardless, physical damage is a common cause of demagnetization.
Corrosion
Another common cause of demagnetization is corrosion. Corrosion can change a magnet’s composition, including the orientation of its atoms. When a magnet begins to corrode, the material from which it’s made will break down.t his degradation can cause the magnet’s atoms to shuffle and become misaligned.
Fortunately, magnets are available with protective coatings to prevent corrosion. You can find them with nickel or zinc coatings, for example. The magnet itself is typically made of a ferromagnetic material like iron, nickel or cobalt, but it features a protective coating to prevent corrosion.
Time
All magnets will gradually lose their magnetic field over time. It’s a process known as magnetic creep. Neodymium magnets typically lose about 1% of their strength per decade. It’s not a substantial loss of strength, nor is it very fast. Nonetheless, time is a common cause of demagnetization.