Nature Commun. 7, 11443 (2016)

A hundred years ago, Albert Einstein and Wander Johannes de Haas tried to confirm the theory of molecular currents proposed by André-Marie Ampère to explain magnetism. They found that an iron cylinder suspended by a string inside a coil started to rotate when an electric current was turned on. This observation relating spin and mechanical angular momentum became known as the Einstein–de Haas effect. But if the iron cylinder in the original experiment were replaced with a single spin, would the total angular momentum still be conserved?

Marc Ganzhorn and colleagues studied such a quantum version of the Einstein–de Haas effect using a single-molecule magnet attached to a carbon nanotube mechanical nanoresonator. They found that for individual spins, the total angular momentum and energy were indeed conserved, and this manifested itself as a complete suppression of the quantum tunnelling of magnetization. The suppression was independent of external noise factors, suggesting that it could become useful in molecular spintronics.