The Barnett effect is the magnetization of an uncharged body when spun on its axis.
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.