Barnett effect

{{Short description|Magnetization of an uncharged body when spun on its axis}}

The Barnett effect is the magnetization of an uncharged body when spun on its axis.{{cite book |title=The Cold Universe |author=Bruce T. Draine |editor1=Andrew W. Blain |editor2=F. Combes |editor3=Bruce T. Draine |editor4=D. Pfenniger |editor5=Yves Revaz |page=276 |chapter-url=https://books.google.com/books?id=A6ceYPsxsSEC&pg=PA276 |isbn=3-540-40838-X |year=2003 |chapter=§7.3 Barnett effect |publisher=Springer}} It was discovered by American physicist Samuel Barnett in 1915.{{cite journal

| last = Barnett | first = S. J.

| title = Magnetization by Rotation

| year = 1915

| journal = Physical Review

| volume = 6 | issue = 4 | pages = 239–270

| doi = 10.1103/PhysRev.6.239

|bibcode = 1915PhRv....6..239B }}

An uncharged object rotating with angular velocity {{math|ω}} tends to spontaneously magnetize, with a magnetization given by

: $M\; =\; \backslash chi\; \backslash omega\; /\; \backslash gamma,$

where {{math|γ}} is the gyromagnetic ratio for the material, {{math|χ}} is the 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.