Updated: Jun 23, 2018
Two common types of magnets go into microphones and speakers: Neodymium and Alnico.
You know those magnets that stick to the fridge so hard you can barely get em off? Those are sometimes called rare-earth but the correct term is Neodymium. (Knee-oh-DIM-ee-um) Useful in speakers because the magnet can be much lighter making the speaker and cabinet a LOT easier
to stuff in the ol Miata. Engineers can easily get more output from a microphone and the sound is often more lively. Shure Beta, EV N/D series, and Miktek PM9 are examples.
Alnico is short for an alloy of Aluminum-nickle-cobalt. A much older technology, but a very stable and reliable one. Hundreds of models of dynamic mics use these types of magnets.
Now you know.