Ferromagnetic metals are those attracted to magnets, the best-known being iron, nickel and rare earth alloys. Other metals are attracted by a different, weaker type of magnetism -- too faint for you to feel -- which is known as paramagnetism.
Ferrous metals include iron and alloys of iron, such as steels. Magnets attract them because their electrons -- and the magnetic fields surrounding those electrons -- tend to easily align with an external magnetic field. Magnets are made from iron by inducing a strong magnetic field to align the atoms and their electrons into one unified magnetic field, which remains after the field is removed. This is called ferromagnetism. Some steel alloys, such as stainless steel, lose this property, so a magnet will not attract them.
Nickel and Nickel Alloys
Elemental nickel is ferromagnetic, as are some -- but not all -- nickel alloys. "Alnico" magnets encompass a group of iron alloys made up of aluminum, cobalt and nickel along with iron. But a magnet will not attract the 25-percent-nickel/75-percent-copper alloy in a U.S. 5-cent piece called a "nickel," nor will it attract stainless steels, which are nickel/steel alloys of various compositions including other elements. However, sometimes processing stainless steel will alter its molecular structure so a magnet will attract it.
Rare Earth Metals and Alloys
Neodymium alloy magnets (also called "NIB" for neodymium, iron and boron) are the strongest rare-earth permanent magnets available today. Samarium-cobalt magnets were developed earlier, but they're not as strong. Ratios of samarium to cobalt vary to produce magnets with different characteristics. Large rare-earth magnets can attract each other with enough force to present a crushing hazard to people handling them, with the added risk of shattering to fragments upon impact.
Metals With Weak Attraction to Magnets
Some metals, such as aluminum, copper and gold, exhibit paramagnetism, where, in the presence of a magnet's field, the metal develops its own magnetic field that attracts it to the magnet by a very weak force. The opposite condition is called diamagnetism, where the metal resists the magnetic field. Unlike with ferromagnetism, in paramagnetism, the magnetic field does not remain after the outside magnetic field is removed.