How To Demagnetize a Magnet

Demagnetizing Permanent Magnets

Long range ordering is what makes a magnet magnetic. If you disrupt the order, you weaken or destroy the magnetic field.
Long range ordering is what makes a magnet magnetic. If you disrupt the order, you weaken or destroy the magnetic field. Andrew Brookes, Getty Images

A magnet forms when the magnetic dipoles in a material orient in the same general direction. Iron and manganese are two elements that can be made into magnets by aligning the magnetic dipoles in the metal, otherwise these metals are not inherently magnetic. Other types of magnets exist, such as neodymium iron boron (NdFeB), samarium cobalt (SmCo), ceramic (ferrite) magnets, and aluminum nickel cobalt (AlNiCo) magnets.

These materials are called permanent magnets, but there are ways to demagnetize them. Basically, it's a matter of randomizing the orientation of the magnetic dipole. Here's what you do:

Demagnetize a Magnet by Heating or Hammering

If you heat a magnet past the temperature called the Curie point, the energy will free the magnetic dipoles from their ordered orientation. The long range order is destroyed and the material will have little to no magnetization. The temperature required to achieve the effect is a physical property of the particular material.

You can get the same effect by repeatedly hammering a magnet, applying pressure, or dropping it on a hard surface. The physical disruption and vibration shake the order out of the material, demagnetizing it.

Self Demagnetization

Over time, most magnets naturally lose strength as long range ordering is reduced. Some magnets don't last very long, while natural demagnetization is an extremely slow process for others.

If you store a bunch of magnets together or randomly rub magnets against each other, each will affect the other, changing the orientation of the magnetic dipoles and lessening the net magnetic field strength. A strong magnet can be used to demagnetize a weaker that has a lower coercive field.

Apply AC Current To Demagnetize a Magnet

One way to make a magnet is by applying an electrical field (electromagnet), so it makes sense you can use alternating current to remove magnetism, too.

To do this, you pass AC current through a solenoid. Start with a higher current and slowly reduce it until it's zero. Alternating current rapidly switches directions, changing the orientation of the electromagnetic field. The magnetic dipoles try to orient according to the field, but since it's changing, they end up randomized. The core of the material may retain a slight magnetic field due to hysteresis.

Note you can't use DC current to achieve the same effect because this type of current only flows in one direction. Applying DC might not increase the strength of a magnet, like you might expect, because its unlikely you'll run the current through the material in the exact same direction as the orientation of the magnetic dipoles. You will change the orientation of some of the dipoles, but probably not all of them, unless you apply a strong enough current.

A Magnetizer Demagnetizer tool is a device you can purchase which applies a strong enough field to change or neutralize a magnetic field. The tool is useful for magnetizing or demagnetizing iron and steel tools, which tend to retain their state unless disturbed.

Format
mla apa chicago
Your Citation
Helmenstine, Anne Marie, Ph.D. "How To Demagnetize a Magnet." ThoughtCo, Jan. 14, 2016, thoughtco.com/how-to-demagnetize-a-magnet-607873. Helmenstine, Anne Marie, Ph.D. (2016, January 14). How To Demagnetize a Magnet. Retrieved from https://www.thoughtco.com/how-to-demagnetize-a-magnet-607873 Helmenstine, Anne Marie, Ph.D. "How To Demagnetize a Magnet." ThoughtCo. https://www.thoughtco.com/how-to-demagnetize-a-magnet-607873 (accessed January 19, 2018).