The curie point, also called the curie temperature, is the temperature at which a ferromagnetic metallic material changes from the ferromagnetic state into the non-magnetic state. Two well-known examples are iron, with a curie point of 770 °C, and nickel, with a curie point of 354 °C.[1]
Physically, this change is a consequence of thermal energy overcoming the magnetic exchange interaction between the atomic magnetic moments inside the material. Below the curie point, these moments stay aligned and give the material its spontaneous magnetization. Above the curie point, thermal agitation randomizes the alignment, the spontaneous magnetization collapses, and the material behaves as a paramagnet instead.
Why the curie point matters in foundry practice
For foundries and metal processing, the curie point is a practical reference temperature in several everyday situations. In scrap sorting, magnetic separators pull iron and steel out of mixed scrap streams because these materials are ferromagnetic; this only works reliably below the curie point, so overheated ferrous scrap can pass a magnetic separator without being captured. In induction heating, the curie point is sometimes used deliberately: the ability of a ferromagnetic workpiece to absorb energy from an alternating magnetic field changes sharply once it passes through its curie point, which is the basis of self-regulating induction and resistance heating elements. In quality control, magnetic particle inspection, a widely used non-destructive testing method for castings and forgings, depends on the ferromagnetic response of the component and therefore only functions while the part stays below its curie point.
Curie points of ferromagnetic metals
| Metal | Curie point |
|---|---|
| Iron | 770 °C |
| Nickel | 354 °C |
| Cobalt | approx. 1,115 °C |
Frequently asked questions
What is the curie point of iron?
Iron has a curie point of 770 °C. Below this temperature iron is ferromagnetic; above it, iron becomes paramagnetic and no longer shows spontaneous magnetization.
Why does magnetism disappear above the curie point?
Above the curie point, thermal energy is high enough to disrupt the alignment of atomic magnetic moments that gives ferromagnetic materials their spontaneous magnetization. Once this alignment breaks down, the material behaves as a paramagnet and no longer retains magnetism on its own.
How is the curie point used in foundries?
In foundries, the curie point serves as a practical reference temperature, for example when sorting ferrous scrap with magnetic separators, when designing self-regulating induction heating processes, or when carrying out magnetic particle inspection on castings, since all of these methods only function while the material remains ferromagnetic.
Related standards
Internationally, the characterization of magnetic materials is covered by the IEC 60404 series of standards, which defines classification and measurement methods for soft and hard magnetic materials.[2]
Sources
- Kittel, C.: Introduction to Solid State Physics. 8th edition, John Wiley & Sons, 2005, Chapter 12 “Ferromagnetism and Antiferromagnetism”, p. 329, Table 1 “Ferromagnetic crystals” (iron 1043 K, nickel 627 K, cobalt 1388 K). Retrieved 2026-08-26.
- IEC 60404-1 et seq., Magnetic materials. International Electrotechnical Commission, series in force.
Related topics
The curie point is closely linked to other temperature-related concepts in foundry practice. See also temperature, temperature gradient, solidification temperature, and raw iron for related metallurgical background.