The Barnett effect is the magnetization of an uncharged body when spun on its axis. It was discovered by American physicist Samuel Barnett in 1915. An uncharged object rotating with angular velocity tends to spontaneously magnetize, with a magnetization given by :

M = \chi \omega / \gamma,

where is the gyromagnetic ratio for the material, is the magnetic susceptibility. The magnetization occurs parallel to the axis of spin. Barnett was motivated by a prediction by

Owen Richardson Sir Owen Willans Richardson, FRS (26 April 1879 – 15 February 1959) was a British physicist who won the Nobel Prize in Physics in 1928 for his work on thermionic emission, which led to Richardson's law. Biography Richardson was born in Dew ...

in 1908, later named the

Einstein–de Haas effect The Einstein–de Haas effect is a physical phenomenon in which a change in the magnetic moment of a free body causes this body to rotate. The effect is a consequence of the conservation of angular momentum. It is strong enough to be observable in ...

, 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.

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