Which metal is commonly used in electromagnet?

Answer 1

From the wikipedia article: http://en.wikipedia.org/wiki/Electromagnet

A coil forming the shape of a straight tube, a helix (similar to a corkscrew) is called a solenoid; a solenoid that is bent into a donut shape so that the ends meet is a toroid. Much stronger magnetic fields can be produced if a "core" of ferromagnetic material, such as soft iron, is placed inside the coil. The core magnifies the magnetic field to thousands of times the strength of the field of the coil alone. This is called a ferromagnetic-core or iron-core electromagnet.

I will assume that you wish to know the metal that is commonly employed as the core, this depends on the application of the magnet but Soft iron is used for many applications. An easy way to produce a electromagnet is using some copper wire, an iron nail and a battery.

For further information on which metal is usually used for cores of magnets can be found at the wikepedia site: http://en.wikipedia.org/wiki/Magnetic_core#Common_magnetic_core_materials.