How to Remagnetize Magnets
Steel or ceramic magnets that have been stored incorrectly, dropped repeatedly or are simply old may lose their magnetic properties. For optimal results when it comes to rejuvenating these magnets, touch one pole to the opposite pole of a neodymium magnet.
Obtain the Materials
Obtain a neodymium magnet, which is made of neodymium, iron and boron. You can purchase them through online retailers (xinyic1.sg-host.com), or at a science supply store. Choose a magnet whose shape will clearly indicate its magnetic polarity, north and south. Bar magnets are good examples; with a spherical magnet, it’s harder to tell which “end” is north or south. Also, avoid the strongest neodymium magnets; though they have important uses in science and industry, their powerful magnetic fields can make them dangerous to handle, especially in the presence of iron or steel objects.
Determine the Neodymium Magnet’s Poles
If it poles are not already marked, identify the neodymium magnet’s north and south poles by placing a compass close to the magnet in question. The needle of the compass will point directly south when brought in close contact with the north pole of the neodymium magnet. Similarly, the needle of the compass with point directly north when brought in close contact with the south pole of the magnet. Use a felt-tipped marker to label the north and south poles of the neodymium magnet for future use. In cases where the magnet comes from the manufacturer already marked with north and south poles, this step will not be necessary.
Determine the Old Magnet’s Poles
Determine the north and south poles of the old magnet that requires remagnetization. To do this, use the compass method described above. As with neodymium magnets, the poles of some steel or ceramic magnets may already be labeled when they come from the manufacturer, thus eliminating the need for this step.
Position Poles Properly
Touch the north pole of the old magnet to the south pole of the neodymium magnet. Repeat the process, this time touching the south pole of the old magnet to the north pole of the neodymium magnet. You may want to repeat this step several times in cases where the old magnet is especially demagnetized.
Storing Your Magnets
Once you’ve remagnetized your magnets, store them such that their poles alternate, i.e. the north pole of one magnet against the south pole of the next. The magnets will naturally attract each other in this orientation, and storing them in this manner helps preserve their magnetic strength. By contrast, storing them in a random jumble or with like poles against each other (north facing north), magnets will deteriorate relatively quickly.
Are they strong?
No. They are not nearly as strong as a neodymium magnet in several important ways. First, let’s consider pull force. The pull force is much, much weaker than a neodymium magnet. Depending on how you measure it, a neodymium magnet is going to be roughly 7-20 times stronger than a flexible magnet of the same size. In some cases, this number can be even higher.
Of course, flexible magnets don’t have to be very strong to just hold themselves on the back of your car. They’re not lifting very much. They don’t stick out into the wind. They are really great for funny bumper “stickers.” Just don’t expect to lift heavy weights with one.
Longtime readers of our blog know that pull force isn’t the only important measure of a magnet’s strength. Coercivity is also key. Coercivity is a magnet’s resistance to getting demagnetized by a magnetic field. The greater the coercivity, the stronger magnetic field you need to magnetize (or de-magnetize) it.
For example, rubbing a strong magnet across a credit card’s magnetic strip can erase the information on it. That’s because the strip’s coercivity is low. It is unable to resist the magnetizing field from the magnet.
Flexible magnets are the same way. Because their coercivity is low, they’re easily influenced by a powerful neodymium magnet.
How does that work?
Stack of ring magnets on a screw, repelling with like poles facing one another.
Now that the stack is assembled, let’s visualize what the field looks like right near the curved surface of the cylindrical stack of magnets. The black lines of flux indicate the field direction at a given point. The field direction is parallel to those black lines.
If you move from left to right along the surface, you see the field direction changing. In the lower picture, the green arrows show the field direction. Say, that looks a lot like a Halbach array!
If we roll or slide a flexible magnet right up against this stack of neodymium magnets, the flexible magnet will “see” that strong magnetic field in the directions shown. After the stack of neodymium magnets are slid away, the flexible magnet retains magnetization in those directions.