Magnetic materials play an important role in key technologies within today's society. Generally speaking there are two types of magnetic devices used. Permanent magnets are materials that naturally produce a magnetic field. Electromagnets are permanent magnets with an electrical conductor coiled around them many times. Depending upon the specific application it can be advantageous to use electromagnets, or permanent magnets.
Advantages of Permanent Magnets
Permanent magnets naturally produce a magnetic field and hence do not need power supplies or wires. Since they do not need power supplies they are energy efficient, and environmentally friendly. Furthermore, they can be made very small, to fit inside compact devices such as electrical motors.
Disdvantages of Permanent Magnets
Permanent magnets only produce magnetic fields below a certain temperature. This can limit the use in applications where the device gets very hot. Some types of permanent magnet corrode over time, which will generally reduce the maximum magnetic field achievable. The magnetic field that a permanent magnet produces can not be changed --- it's an intrinsic property of the material. Applications that require a changing magnetic field would be better suited to electromagnets
Advantages of Electromagnets
Electromagnets are permanent magnets that have been coiled with a metallic wire such as copper. When current is passed through the wire, a field is produced in the permanent magnet which enhances the external magnetic field produced.
The magnetic field produced is dependent on some variables that can be changed relatively easily such as number of coil turns, and the amount of current applied to the coil. Hence, electromagnets can be designed to produce particular fields. A further advantage of electromagnets is possibility of changing the magnetic field over a period of time. This can be achieved by simply changing the current supplied to the coil, allowing the electromagnet to be switched on and off.
Disadvantages of Electromagnets
Electromagnets require a significant amount of copper coiling to reach the desired fields. This generally means they are unsuited to applications where there is little space. The application of too large a current to the coiling can create a short; leaving the electromagnet useless unless it is recoiled.