Question

Do magnets ever lose their magnetism?

Asked by: Kevin H.

Answer

Yes, it is possible for a permanent magnet to lose its magnetism. There are three common ways for this to occur:

1) Via heat: ferromagnet materials will lose their magnetism if heated above a point known as the Curie temperature. At this point, the energy being put into the magnet from the heat will permanently disrupt the magnetic domain structure of the material, turning it into a paramagnetic material [a similar effect occurs in materials called hard ferrites, which exhibit a form of magnetism called ferrimagnetism; the analogous temperature for these materials is known as the Neel point]. You would have to re-magnetize the magnet again, either in a solenoid or with another permanent magnet, in order to restore the magnetism. If you heat a magnet up a little bit, it will lose some of its magnetism, but on returning to room temperature [depending on how high it was heated, and on the shape of the magnet itself], full magnetism can be restored.

2) Via a demagnetizing magnetic field: permanent magnets exhibit a characteristic called coercivity, which is the ability of a material to withstand being demagnetized by an applied magnetic field. Modern permanent magnet materials such as Sm-Co and Nd-Fe-B have high coercivities; older materials such as Alnico or ceramic [hard ferrite] materials have lower coercivities. With a strong enough magnetic field of opposite polarity, it is therefore possible to demagnetize the magnet [whether this comes from another permanent magnet, or a solenoid]. Interestingly, an opposing magnetic field is sometimes applied to a magnet in order to 'knock it down', or to lower its overall magnetic output, so that it can be used appropriately in an application.

3) Via shock: this really only applies to older materials such as magnetic steels and Alnico materials; the mechanism that creates coercivity means that they are susceptible to being demagnetized if enough energy is transmitted through the material via a shock, such as being dropped or hit with a hammer. Modern materials do not suffer this type of problem.

Answered by: Gareth Hatch, Ph.D., Director of Technology - Dexter Magnetic Technologies

Search

Loading


Support Discovery Capsule - Anton's new project on Kickstarter.



Science Quote

'Science is a refinement of everyday thinking.'

Albert Einstein
(1879-1955)
Science Sidebar | Science Education Articles
Cool Summer Science Projects

Why not make science a part of your family’s summer? Perhaps you can set aside one day a week for outdoor projects—maybe Mad Scientist Monday or Scientific Saturday? Here are a few ideas to help get you started. Continue reading ...

10 Ways to Keep Your Kids Interested In Science

Young children are natural scientists: they ask questions, pick up sticks and bugs outside, and are curious about the world around them. But as they get a bit older, many kids gradually lose their interest in science. They might see it as just another task at school, something that doesn't apply to their lives. Of course nothing could be further from the truth, so here are ten ways you can remind your kids that science is everywhere. Most of these are fun for adults, too! Continue reading ...

Top Selling

Here are our physics & astronomy bestsellers:
Magnetic Levitator - Classic
Revolving Multi-Color Fiberoptic Light
Scorpion, Ant, Wasp and Flower Bug
12 inch Galileo Thermometer
Solar Radiometer
Enviro Battery 4M Kit
Wood Grain Newtons Cradle
Brush Robot 4M Kit
Tin Can Robot 4M Kit
Electric Plane Launcher 4M Kit

Sponsors

USC University of Southern California Dornsife College Physics and Astronomy Department McMaster University Physics and Astronomy Department