The five families, side by side
| Material | Formula | Strength | Max operating temperature | Cost | Corrosion |
|---|---|---|---|---|---|
| Neodymium | NdFeB | Strongest available | 80 °C standard, up to ~200 °C in high-temperature grades | Moderate | Poor — almost always plated |
| Samarium cobalt | SmCo | Strong — below neodymium | 250–350 °C | High | Excellent — usually needs no plating |
| Alnico | AlNiCo | Moderate | 450–550 °C | Moderate to high | Good |
| Ferrite (ceramic) | SrFe / BaFe | Low | up to ~250 °C | Lowest | Excellent |
| Flexible / bonded | polymer-bonded | Very low | typically below 80 °C | Low | Good |
Read the temperature column first. Most specifying mistakes are
temperature mistakes. A neodymium magnet that is perfect on the bench will quietly lose
strength it never gets back the first time the housing runs hot, and nothing about its
appearance will tell you it has happened.
Neodymium
NdFeB
The strongest permanent magnet you can buy, and the default choice unless heat or corrosion rules it out.
Samarium cobalt
SmCo
What you use when it gets too hot for neodymium, or too wet.
Alnico
AlNiCo
The high-temperature option, and the one that will happily demagnetise if treated carelessly.
Ferrite (ceramic)
SrFe / BaFe
Cheap, weak, and almost impossible to damage with weather. Most loudspeakers and holding magnets are these.
Flexible / bonded
polymer-bonded
Magnetic powder in rubber or plastic. Weak by design, and the only type you can cut with scissors or mould into a shape.
A shorter way to decide
If it stays cool and indoors, use neodymium and pick the grade by how much force you need. If it gets hot, go to samarium cobalt, or alnico if it gets very hot. If it lives outside and the force is modest, ferrite will outlast everything else and cost the least. If it has to bend or be cut to shape, it is flexible sheet and you should not expect much holding force from it.
None of that answers what shape the field should be, which is the part the catalogue deals with — whether the magnet should hold, align, latch, spring or release.