The magnetic stirrer is a device used to create a rotating magnetic field.  A magnetic stirrer is often used with hot plates. The stir bar is the magnetic bar that is immersed in the liquid to provide the stirring action. A magnetic stirrer is a device used to create a rotating magnetic field. The magnetic stirrer creates a rotating field based on a rotating magnet bar or a plate containing the rotating magnet. In general, the bar magnet is coated with plastic and the plate contains a rotating magnet. It is possible to create a rotating magnetic field with the help of a rotating magnet.