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In physics and materials science, the Curie temperature (T C), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can (in most cases) be replaced by induced magnetism. The Curie temperature is named after Pierre Curie, who showed that magnetism is lost at a critical temperature. [1]
Although they have higher remanence and much higher coercivity and energy product, neodymium magnets have lower Curie temperature than many other types of magnets. That Nd 2 Fe 14 B maintains magnetic order up to beyond room temperature has been attributed to the Fe present in the material stabilising magnetic order on the Nd sub-lattice. [15]
In magnetism, the Curie–Weiss law describes the magnetic susceptibility χ of a ferromagnet in the paramagnetic region above the Curie temperature: = where C is a material-specific Curie constant, T is the absolute temperature, and T C is the Curie temperature, both measured in kelvin.
Hence the magnetization of an anisotropic magnet is harder to destroy at low temperature and the temperature dependence of the magnetization deviates accordingly from the Bloch T 3/2 law. All real magnets are anisotropic to some extent. Near the Curie temperature, (),
is the magnitude of the applied magnetic field (A/m), is absolute temperature , is a material-specific Curie constant (K). Pierre Curie discovered this relation, now known as Curie's law, by fitting data from experiment. It only holds for high temperatures and weak magnetic fields.
Rare-earth magnets have higher remanence, much higher coercivity and energy product, but (for neodymium) lower Curie temperature than other types. The table below compares the magnetic performance of the two types of rare-earth magnets, neodymium (Nd 2 Fe 14 B) and samarium–cobalt (SmCo 5), with other types of permanent magnets.
Alnico alloys have some of the highest Curie temperatures of any magnetic material, around 800 °C (1,470 °F), although the maximal working temperature is typically limited to around 538 °C (1,000 °F). [4] They are the only magnets that have useful magnetism even when heated red-hot. [5]
When cooled below a temperature called the Curie temperature, the magnetization of a piece of ferromagnetic material spontaneously divides into many small regions called magnetic domains. The magnetization within each domain points in a uniform direction, but the magnetization of different domains may point in different directions.