Q.Do they demagnetize over time?
Magnets > Magnets > Ferrite Magnets/ Neodymium Magnets
In addition to initial demagnetizing, there is also gradual demagnetizing over time. The amount of change depends on factors such as the permeance coefficient, operating temperature, and material of the magnet, and changes generally tend to occur more with compact and thin products because size and shape are also factors.
However, the amount of change practically has no affect most of the time because measures for changes over time are taken.