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.

Why You Would Want to Demagnetize a Magnet

You may be wondering why you'd want to ruin a perfectly good magnet. The answer is that sometimes magnetization is undesirable. For example, if you have a magnetic tape drive or other data storage device and wish to dispose of it, you don't want just anyone to be able to access the data. Demagnetization is one way to remove the data and improve security.

There are many situations in which metallic objects become magnetic and cause problems. In some cases, the problem is that the metal now attracts other metals to it, while in other cases, the magnetic field itself presents issues. Examples of materials that are commonly demagnetized include flatware, engine components, tools (although some are intentionally magnetized, like screwdriver bits), metal parts following machining or welding, and metal moulds.

Key Points

  • Demagnetization randomizes the orientation of magnetic dipoles.
  • Demagnetization processes include heating past the Curie point, applying a strong magnetic field, applying alternating current, or hammering the metal.
  • Demagnetization occurs naturally over time. The speed of the process depends on the material, the temperature, and other factors.
  • While demagnetization may occur by accident, it is often performed intentionally when metal parts become magnetized or in order to destroy magnetic-encoded data.