The magnetic stirrer consist of magnetic stir plate and magnetic stir bar. The stir plate is to provide the rotating field by permanent magnet or a set of stationary electromagnets. And then this rotating external magnetic field will spin the magnetic stir element placed in the container.
What stir magnet can be used on magnetic stir rod?
The magnetic stir rod is made with permanent magnets encased in material that won’t react with the fluid it is immersed in, such as Parylene, PTFE (a.k.a. Teflon). The stirring magnets are available in permanent Alnico magnets, ceramic magnets, rare earth neodymium magnets and samarium cobalt magnets.
Ceramic magnets are cheap and common, but not nearly as strong as a neodymium magnet. They have only about 8-10% of the pull force.
Alnico magnets are stronger than ceramic magnets, about 25% of the strength of a neodymium magnet of the same size. They have been commonly used for stir bars, especially for high temperature use. With very low coercivity, alnico magnets are easiest to demagnetize. If exposed to a strong magnetic field, they can become weaker.