What is Curie Temperature and Why Does It Matter to Magnets?

Magnet Applications
What is Curie Temperature and Why Does It Matter to Magnets-Bunting-DuBois-Magnet Applications

When discussing magnets and magnetic properties, the term “Curie temperature” or “Curie point” is frequently mentioned. The Curie temperature is defined as the maximum temperature a material can reach before it loses its magnetic properties. When a magnetic material reaches its Curie temperature, the spontaneous magnetization in the material drops to zero. At this point, it will no longer be a ferromagnetic material, and will instead become a paramagnetic material.

To explain the difference between ferromagnetic and paramagnetic materials, we must return to what creates the force of magnetism in a material in the first place. A material’s force of magnetism is determined by its magnetic moment, which is a dipole moment within in atom originating from the spin and angular momentum of electrons. Different materials have different structures of intrinsic magnetic moments, and the alignment of these intrinsic magnetic moments is dependent on temperature.

When a material reaches its Curie temperature, it has reached a critical point when the intrinsic magnetic moments within it change direction.

In order for a material to be magnetic, its magnetic moments must be aligned in a specific way. Induced magnetism, then, is created when a collection of disordered magnetic moments are forcibly aligned in an applied magnetic field. When a material reaches its Curie temperature, its alignment of magnetic moments is forcibly made to be disordered. Following this principle, as materials are exposed to increasingly higher temperatures, their magnetic strength weakens as the temperature moves closer to the material’s Curie temperature and magnetic moments begin to shift out of alignment. As a general rule, magnets are weaker when exposed to higher temperatures.

Different types of magnets have different maximum operating temperatures. A material’s Curie temperature is one of the variables that determines the maximum operating temperature of any given magnetic material.

Maximum operating temperature is an extremely important factor to consider when selecting a magnet for an application. Typically, strength is considered the most important trait of a magnet, but a magnet that becomes demagnetized as a result of high operating temperatures ends up with no strength at all. Alnico magnets have the highest maximum operating temperature, and can tolerate temperatures between 450-900°C. Samarium cobalt magnets, a type of powerful rare earth magnet, have the second highest maximum operating temperature, and can tolerate temperatures between 250-350°C. Standard neodymium magnets have a maximum operating temperature of 80°C, although high temperature neodymium magnets can be used at operating temperatures from 140-200°C. Finally, ceramic magnets have a maximum operating temperature of up to 300°C.

When selecting a magnet for any given application, the operating temperature must be taken into consideration. Each magnet material has a different maximum operating temperature, and all magnets weaken in strength as they exposed to higher temperatures. For more information on selecting the appropriate magnet material for your application, contact Bunting-DuBois today.