Before we explain how magnets demagnetize – lose their magnetism, it may be helpful to note:
Permanent magnets are made of elements known as ferromagnetic materials by exposing them to a magnetic field using electric current. Using a magnetizing fixture that directs current through the non-magnetized part, electron spins in these metals are lined up, or polarized, making the material magnetic.
Magnets can lose their magnetism, or demagnetize, in a few different ways:
• Heat: When exposed to high temperatures, the tiny magnetic regions within the material, called magnetic domains, vibrate more energetically. This vibration disrupts the alignment of these domains, weakening or even destroying the magnet’s overall magnetic field. The specific temperature at which this happens, called the Curie temperature, varies depending on the material the magnet is made of.
• Cold: Some magnet materials lose their ability to resist demagnetization at cold temperatures. Ceramic/Hard Ferrite materials are at risk at temperatures below -40°C (-40°F) and Neodymium Iron Boron has problems below -138°C (-216°F). Neither Alnico nor Samarium Cobalt experience this effect and they can be used down to near Absolute Zero, -273°C (-460°F)
• Strong magnetic fields: Exposing a magnet to a strong magnetic field in the opposite direction of its own magnetism can also disrupt the alignment of its internal domains. This can happen accidentally, for example, if you bring a strong magnet close to another magnet. Degaussing, a technique used to intentionally remove magnetism from objects, also works on this principle by applying a strong, alternating magnetic field.
• Time: While less common, even at room temperature, thermal vibrations can very slowly misalign the magnetic domains, causing a gradual weakening of the magnet’s field over extended periods, typically over decades. This process is much slower than the other methods mentioned above.
It’s important to note that demagnetization can be reversible or irreversible depending on the severity of the cause and the type of magnet. In some cases, simply removing the magnet from the heat source or the strong magnetic field can allow the domains to realign and regain some or all of its magnetism. However, in other cases, the damage might be permanent.
Tags: demagnetization, how do magnets demagnetize