Barnett effect

The Barnett effect is the magnetization of an uncharged body when spun on its axis.[1] It was discovered by American physicist Samuel Barnett in 1915.[2]

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

${\displaystyle M=\chi \omega /\gamma \ ,}$

with γ = gyromagnetic ratio for the material, χ = magnetic susceptibility.

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, 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.

See also

• London moment

References

1. Bruce T. Draine (2003). "§7.3 Barnett effect". In Andrew W. Blain; F. Combes; Bruce T. Draine; D. Pfenniger; Yves Revaz (eds.). The Cold Universe. Springer. p. 276. ISBN 3-540-40838-X.
2. Barnett, S. J. (1915). "Magnetization by Rotation". Physical Review. 6 (4): 239–270. Bibcode:1915PhRv....6..239B. doi:10.1103/PhysRev.6.239.

Further reading

• S. J. Barnett, Gyromagnetic and Electron-Inertia Effects, Review of Modern Physics, Vol. 7, Issue 2, pp. 129–166 (1935)