Short answers, pulled from the story.
The Einstein, de Haas effect describes how a change in the magnetic moment of a free body causes that body to rotate. This physical phenomenon serves as a direct consequence of the conservation of angular momentum.
Albert Einstein and Wander Johannes de Haas published two papers containing descriptions of expected results and measurements in April 1915. Einstein announced the work in a report to the German Physical Society on the 7th of May 1915 stating experiments firmly established existence of molecular currents.
Owen Willans Richardson derived an expected relation of g equals one point zero before electron spin was discovered in 1925. Later measurements demonstrated that the gyromagnetic ratio for iron is indeed close to two rather than one, with pure iron showing a value of g equals two point zero.
Later accurate experiments revealed that ninety-six percent of magnetization in pure iron arises from polarization of electron spins while only four percent stems from orbital angular momentum polarization. These findings allow scientists to separate contributions from electron spin and orbital motion within ferromagnetic materials like iron.
Geertruida de Haas-Lorentz donated the experimental equipment to the Ampère Museum in Lyon France in 1961. The equipment went lost and was later rediscovered in 2023 after being missing for over six decades.