The Hopkinson effect is a feature of

ferromagnetic Ferromagnetism is a property of certain materials (such as iron) which results in a large observed magnetic permeability, and in many cases a large magnetic coercivity allowing the material to form a permanent magnet. Ferromagnetic materials ...

ferrimagnetic A ferrimagnetic material is a material that has populations of atoms with opposing magnetic moments, as in antiferromagnetism, but these moments are unequal in magnitude so a spontaneous magnetization remains. This can for example occur when ...

materials, in which an increase in

magnetic susceptibility In electromagnetism, the magnetic susceptibility (Latin: , "receptive"; denoted ) is a measure of how much a material will become magnetized in an applied magnetic field. It is the ratio of magnetization (magnetic moment per unit volume) to the ap ...

is observed at temperatures between the blocking temperature and the

Curie temperature 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 Cur ...

of the material. The Hopkinson effect can be observed as a peak in thermomagnetic curves that immediately precedes the susceptibility drop associated with the Curie temperature. It was first observed by

John Hopkinson John Hopkinson, FRS, (27 July 1849 – 27 August 1898) was a British physicist, electrical engineer, Fellow of the Royal Society and President of the IEE (now the IET) twice in 1890 and 1896. He invented the three-wire ( three-phase) system fo ...

in 1889 in a study on iron.Hopkinson, John. “Magnetic and Other Physical Properties of Iron at a High Temperature”. Philosophical Transactions of the Royal Society of London. A 180 (1889): 443–465. In single domain particles, a large Hopkinson peak results from a transient

superparamagnetic Superparamagnetism is a form of magnetism which appears in small ferromagnetic or ferrimagnetic nanoparticles. In sufficiently small nanoparticles, magnetization can randomly flip direction under the influence of temperature. The typical time be ...

particle domain state.

References

Ferromagnetism Rock magnetism vi: Hiệu ứng Hopkinson {{electromagnetism-stub

See also

References