Ferromagnetic materials or substances comprise a small group of substances found in nature, which, when placed in the presence of a magnetic field, are strongly magnetized, and their magnetic field is many times greater than the field that was applied. It is verified that the presence of a ferromagnetic material makes the resulting magnetic field hundreds of times more intense.
With the magnetization of this piece of iron, the resulting magnetic field becomes stronger than the field created by the electric current passing through the coil. In this way, the coil + iron set becomes a very strong electromagnet. Electromagnets are widely used, for example in cranes that transport very heavy loads and in telephone sets.