Re: What types of magnets are there, and what are there definitions

Hi Kelly,

You've asked my favorite kind of question: specific enough to be able to 
answer, but vague enough to let me to be able to come up with all sorts 
of cool science info.  So I'll just ramble for a while, and you pick the 
answer you want.

Answer #1: Two.  Ferromagnets and... um... not.
Ferromagnets 
are any material that can be permanently magnetized.  If you apply a 
magnetic field, then remove it, some of the domains (small zones in the 
material) will remain aligned, creating an internal magnetic field.  
These are the magnets that most people think of when they say magnets.

Non Ferromagnetic materials fall into two categories that aren't very 
different.  
Paramagnetic and  
Diamagnetic materials will magnetize while under a magnetic field but 
it'll go away once the field is removed.  Most materials fall into these 
categories.  (They differ because one is from electron orbitals, and the 
other is from electron spins, but that's a different question.)  Note: 
Any ferromagnetic materials become paramagnetic above their Curie 
temperature.

Answer #2: Two.  Rare Earth and Ceramic.  The two types of magnets you'll 
typically find in any science lab or be able to purchase are going to be 
crumbly ceramic stuff, or a pretty hard metal alloy (rare earth).

Answer #3: Two.  Permanent or Electrical.  Permanent magnets don't 
require any electricity to run.  An electromagnet
 is a paramagnetic material that produces a magnetic field when 
electrical current induces one.  The effect goes away once the power is 
off though.

Answer #4: Lots.  There's Ferrite, Alnico (Aluminum-Nickel-Cobalt), SmCo 
(Samarium Cobalt), NIB (Neodymium-Iron-Boron), Europium Oxide, Yttrium-
Iron-Oxide, Gadolinium, Dysprosium, Manganese-Arsenic, and many others.  
These differ in their magnetic strength, material strength and 
brittleness, cost, Curie temperature, and a bunch of other stuff.  If you 
want more specific info on their differences, here is a table of 
Curie Temperatures; here is a description 
and rating of different types; and here is a list of 
frequently asked questions.

Other cool links:
Magnet University
Cool Magnet info, 
pictures, and extra cool links
Analysis of medicinal magnet 
therapy

I hope this helps!
Jeff Yap
Mad Scientist