How are magnets made?
Modern magnet materials are made through casting, pressing and sintering, compression bonding, injection molding, extruding, or calendering processes.
How permanent is a magnet's strength?
If a magnet is stored away from power lines, other magnets, high temperatures, and other factors that adversely affect the magnet, it will retain its magnetism essentially forever.
Will magnets lose their power over time?
Modern magnet materials do 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.
What might affect a magnet's strength?
The factors can affect a magnet's strength:
Heat
Radiation
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.
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.