Magnetic Power
Will magnets lose their power over time?
Modern magnet materials lose a very small fraction of their magnetism over time. For Samarium Cobalt materials, for example, this has been shown to be less that 1% over a period of ten years. Otherwise, permanent magnets are just that – permanent (you have to do some work to actively try and de-magnetize them).
Can a magnet that has lost its magnetism be re-magnetized?
Provided that the material has not been damaged by extreme heat, magnets can be re-magnetized back to original strength, if they have been exposed to conditions which cause them to become demagnetized.
How do you measure the strength 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 (so it’s easy to compare one magnet to another), and Pull-Testers can measure pull in pounds, kilograms, or other force units. Special Gaussmeters can cost several thousands of dollars. We stock several types of Gaussmeters that cost between $400 and $1,500 each.
If I have a neo magnet with a Br of 12,300 gauss, should 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 Neo magnet that is 1/4” long, will measure approximately 2,500 Gauss 1/16” away from the surface, and 2,200 Gauss 1/8” away from the surface.
Can I make a magnet that I already have any stronger?
Once a magnet is fully magnetized, it cannot be made any stronger - it is "saturated". In that sense, magnets are like buckets of water: once they are full, they can’t get any "fuller".
How Does A Magnet’s Strength Drop Off Over Distance?
The strength of a magnetic field drops off roughly exponentially over distance.
Here is an example of how the field (measured in Gauss) drops off with distance for a Samarium Cobalt Grade 18 disc magnet which is 1” in diameter and 1/2” long.
What Is The Equation For Field Strength Relative To Distance?
For a circular magnet with a radius of R and Length L, the field at the centerline of the magnet a distance X from the surface can be calculated by the following formula (where Br is the Residual Induction of the material):
There are additional formulae that can be used to calculate the field from a rectangular magnet and magnets in other configurations, but the formulae get too long and complex looking to include here!