= Einstein-de Haas effect
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{wiki=Einstein–de_Haas_effect}
The <Einstein-de Haas effect> is mechanical rotation or twisting caused by a change in a body's <magnetization>. The microscopic carriers of <magnetic dipole moment> also carry <angular momentum>: changing their net orientation can transfer <angular momentum> to the body. A freely suspended <ferromagnet> can therefore turn when its <magnetization> reverses. A suspension instead stores part of the response as an elastic twist. This makes a microscopic property accessible through a macroscopic <angle>.
The central measurement compares a change of <magnetic dipole moment> with transferred <angular momentum>, giving a <gyromagnetic ratio>. It complements an ordinary <magnetic dipole torque> measurement: even with the applied <magnetic field> parallel to the suspension axis, so that an ideal axial <magnetic dipole moment> has $\mathbf m\times\mathbf B=\mathbf0$, changing <magnetization> can drive an axial twist. The external drive supplies <energy>; <conservation of angular momentum> still requires accounting for the suspension and any external axial <torque>.
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