How permanent is a magnet’s strength?
If stored away from factors that adversely affect the magnet such as power lines, other magnets, high temperatures etc., a magnet will retain its magnetism essentially forever.
What might affect a magnet’s strength?
Factors that can affect a magnet's strength include:
Strong electrical currents in close proximity to the magnet
Other magnets in close proximity to the magnet
Neo magnets will corrode in high humidity environments unless they have a protective coating.
Shock and vibration do not affect modern magnet materials, unless sufficient to physically damage the material.
Will magnets lose their power over time?
Modern magnet materials do lose a very small fraction of their magnetism over time. With samarium cobalt magnets, for example, this has been shown to be less than 1% over a period of ten years.
Which are the strongest magnets?
The most powerful magnets available today are the rare- earth types. Of the rare-earths, neodymium magnets are the strongest. However, at elevated temperatures (of approximately 150°C and above), samarium cobalt magnets can be stronger than neo magnets, depending on the magnetic circuit.
What are superconductors?
These are the strongest magnets. They don't need a metal core at all, but are made of coils of wire made from special metal alloys which become superconductors when cooled to very low temperatures.
Can I make a magnet that I already have stronger?
Once a magnet is fully magnetized, it's "saturated" and cannot be made any stronger. In that sense, magnets are like buckets of water: once they are full, they can't get any "fuller".
Can a magnet that has lost its magnetism be re-magnetized?
Provided that the material has not been damaged by extreme heat, most magnets can be re-magnetized back to their original strength.
How do you measure the strength or power of a magnet?
Most commonly, Gaussmeters, magnetometers, or pull-testers are used to measure the strength of a magnet. Gaussmeters measure the strength in Gauss; Magnetometers measure in Gauss or arbitrary units (making it easy to compare one magnet to another); pull-testers measure pull in pounds, kilograms, or other force units. Helmholtz Coils, search coils and permeameters are also used to make sophisticated measurements of magnets.
If I have a neo magnet with a Br of 12,300 Gauss, will I be able to measure 12,300 Gauss on its surface?
No. The Br value is measured under closed-circuit conditions. A closed-circuit magnet is not of much use. In practice, you will measure a field that is less than 12,300 Gauss close to the surface of the magnet. The actual measurement will depend on whether the magnet has any steel attached to it, how far away from the surface you make the measurement, and the size of the magnet (assuming that the measurement is being made at room temperature). For example, a 1" diameter Grade 35 neodymium magnet that is ¼" long will measure approximately 2,500 Gauss when 1/16" away from the surface, and 2,200 Gauss when 1/8" away from the surface.