A brand-new neodymium block, straight from production, has no magnetic field at all. A few seconds in a magnetizing coil later, the same block lifts hundreds of times its own weight. The material did not change - what changed is the arrangement of magnetic domains inside it.
What is a magnetic domain?
Inside every magnetic material, atoms act like tiny bar magnets. In an unmagnetized block, these atoms group into small neighborhoods called domains, each pointing in a different direction. Pointing this way and that, they cancel each other out - which is why the block shows no field.
When you magnetize it, a strong external field pushes all the domains to line up in the same direction. Now their effects add up instead of canceling, and the block becomes a magnet.
Why a magnet remembers
Here is the clever part: after the magnetizing field is switched off, the domains stay mostly lined up. The material "remembers" the direction and keeps its strength for decades - that is exactly what makes a permanent magnet permanent.
What scrambles the memory
Domains can be knocked out of line. Strong heat shakes them up; a hard knock or an opposing magnetic field can flip them. Once enough domains point the wrong way, the magnet gets weaker - permanently. That is demagnetization in a nutshell.
| State | What the domains do |
|---|---|
| Unmagnetized | Point in random directions - they cancel |
| Magnetized | Mostly lined up - the magnet holds its strength |
| Overheated / knocked | Some flip back - strength is lost |
Why it matters
Understanding domains explains the three rules every magnet user learns: keep magnets cool, keep them away from strong opposing fields, and store them so they do not knock each other around.
Read on: magnets and heat → · how magnets lose their strength →