Not everything that reacts to a magnet is a "magnet." Every material responds to a magnetic field in some way — but only a few respond strongly enough to be useful, and those are what engineers call magnetic materials.
Three families, one simple idea
The classification comes down to one question: how hard is it to demagnetize? On that basis, magnetic materials split into three families.
Soft magnets are easy to magnetize and just as easy to demagnetize. They don't hold their field — they channel it, which makes them perfect for transformers, motor cores and inductors, where the field flips many times per second. Silicon steel is the classic soft magnet.
Permanent magnets are the opposite. Once magnetized, they stay magnetized, holding their field with no power supply. The harder it is to demagnetize one, the better permanent magnet it makes.
Semi-hard materials sit in between: magnetic enough to hold a state, weak enough to switch. They fill niche roles like reed switches and small hysteresis motors.
The permanent-magnet family tree
When people say "magnets," they usually mean permanent magnets, and the family tree has four main branches — plus one promising newcomer:
| Family | One-line profile |
|---|---|
| Ferrite | Cheap, corrosion-proof, everyday magnets |
| AlNiCo | Oldest family, best heat resistance |
| SmCo (samarium-cobalt) | Rare earth, strong and heat-stable |
| NdFeB (neodymium) | Strongest at room temperature |
| SmFeN | Newcomer, promising, still in research |
Which one do you need?
There is no single "best" magnet. Ferrite wins on price in huge volumes; AlNiCo and SmCo carry the high-temperature jobs; NdFeB wins wherever the smallest, strongest magnet matters — motors, speakers, sensors. The newcomer SmFeN may one day challenge NdFeB, but it is not quite here yet.
Read on: why rare earths make such strong magnets → · the four materials compared →