Barnett Effect
The Barnett effect is the magnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...

ization of an uncharged body when spun on its axis. It was discovered by American physicist Samuel Barnett
Samuel Jackson Barnett
Samuel Jackson Barnett was an American physicist. He was a professor at the University of California, Los Angeles....

 in 1915.

An uncharged object rotating with angular velocity ω tends to spontaneously magnetize, with a magnetization given by:

with γ = gyromagnetic ratio for the material, χ = magnetic susceptibility
Magnetic susceptibility
In electromagnetism, the magnetic susceptibility \chi_m is a dimensionless proportionality constant that indicates the degree of magnetization of a material in response to an applied magnetic field...


The magnetization occurs parallel to the axis of spin. Barnett was motivated by a prediction by Owen Richardson in 1908, later named the Einstein-de Haas effect
Einstein-de Haas effect
The Einstein–de Haas effect, or the Richardson effect , is a physical phenomenon delineated by Albert Einstein and Wander Johannes de Haas in the mid 1910's, that exposes a relationship between magnetism, angular momentum, and the spin of elementary particles...

, that magnetizing a ferromagnet can induce a mechanical rotation. He instead looked for the opposite effect, that is, that spinning a ferromagnet could change its magnetization. He established the effect with a long series of experiments between 1908 and 1915.

Further reading

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