There are three main types of magnets: temporary, permanent, and electromagnets.
Temporary: Some iron and iron alloys can be easily magnetized by even a weak magnetic field. However, when the magnetic field is removed, the object gradually loses its magnetism.
Permanent: Examples are alnico (Aluminum Nickel Cobalt alloy) and ferrites (ceramic-like material that is made from a mix of iron oxides with nickel, strontium, or cobalt). Once they are magnetized, these objects do not easily lose their magnetism.
Electromagnets: These are used when a very strong magnet is necessary. Electromagnets are made by placing a metal core inside a coil of wire that is carrying an electrical current. The electricity going through the wire produces a magnetic field. While the electric current is flowing, the core acts as a strong magnet. Computers, TVs, and electric motors use electromagnets.
The common types of material that permanent magnets are made with are ceramic, alnico, and neodymium. Ceramic magnets are strong, and work well for most experiments. Alnico magnets are even stronger and work very well for science experiments, although they are more expensive than ceramic magnets. Neodymium magnets are so strong that one a half-inch in diameter can lift several pounds of ferromagnetic objects. They are the most expensive of these three magnet types.