How to Neutralize a Permanent Magnet

Magnetic attraction

Permanent magnets are created from ferromagnetic substances. A substance is ferromagnetic if it possesses magnetization outside of the presence of an external magnetic field. The most common types of ferromagnetic substances are iron, nickel and cobalt. If magnetized, these substances become ferromagnets, permanent magnets capable of retaining magnetic properties. Permanent magnets can be neutralized by raising the temperature of the magnet above the Curie point of the substance the magnet is made of. The Curie point is the temperature point beyond which a ferromagnetic material becomes paramagnetic. Paramagnets are only magnetic in the presence of an external magnetic field.

Things You'll Need

• Permanent magnet
• Iron rod
• Concrete slab or flat stone at least 14-by-10-inches
• 2 concrete bricks
• Propane blow torch

Instructions

1. Stand your iron rod vertically on concrete or a flat-surfaced stone. Secure the rod to this makeshift base by placing your concrete bricks on two opposite sides of the rod, sandwiching the rod into a stable vertical position. Ensure the rod is held firmly upright. If a moderate touch or bump will knock it over, it is not secure.

2. Attach your permanent magnet to the iron rod. Because the metal of the permanent magnet is still magnetized, all you have to do to attach the magnet is bring it into contact with the iron rod and magnetic forces will hold it in place.

3. Use your propane blow torch to heat the permanent magnet. How long you need to heat the magnet depends on its size and the type of metal. The Curie point temperature of iron is 1,043 Kelvin (770 centigrade). The Curie point temperature of nickel is 627 Kelvin (358 centigrade). The Curie point temperature of cobalt is 1,388 Kelvin (1,131 centigrade).

4. Keep the heat on the permanent magnet until it falls from the iron rod. It will fall from the iron rod once the temperature of the metal that makes up the permanent magnet reaches its Curie point.

Tips & Warnings

• It is also possible to neutralize a somewhat weak permanent magnet by hammering it or repeatedly dropping it. This jarring action will jumble the coherent ordering within the magnet and further weaken and eventually completely demagnetize the magnet.

• If you would like to purchase a stand and base rather than creating a makeshift stand and base to hold your magnet, use the Physics Learning Laboratories link in the Resources section.

References

• Georgia State University: Ferromagnetism
• University of Illinois: Heating Magnet
• Louisiana State University: Key Ideas About Magnets

Resources

• Physics Learning Laboratories