Einstein's Magnetic Effect Is Measured On Microscale

The Einstein-de Haas effect was first observed in experiments reported in 1915, in which a large iron cylinder suspended by a glass wire was made to rotate by an alternating magnetic field applied along the cylinder's central axis. By contrast, the NIST experiments, described in the Sept. 18 issue of Applied Physics Letters,* measured the Einstein-de Haas effect in a ferromagnetic thin film only 50 nanometers thick deposited on a microcantilever--a tiny beam anchored at one end and projecting into the air. An alternating magnetic field induced changes in the magnetic state of the thin film, and the resulting torque bent the cantilever up and down by just a few nanometers.

Using a laser interferometer to measure the movements of the cantilever and comparing those data to changes in the magnetic state of the material, researchers were able to determine the "magnetomechanical ratio," or the extent to which the material twists in response to changes in its magnetic state. The magnetomechanical ratio is related to another important parameter, the "g-factor," a measure of the internal magnetic rotation of the electrons in a material in a magnetic field.

The magnetomechanical ratio and the g-factor are critical in understanding magnetization dynamics and designing magnetic materials for data storage and spintronics applications, but they are extremely difficult to determine accurately because of many potential complicating effects. The NIST experiments provide a proof-of-concept for using the Einstein-de Haas effect to determine the magnetomechanical ratio and the related g-factor in thin ferromagnetic films. The researchers note that a number of improvements are possible, such as operating the cantilever system in a vacuum to reduce the effects of any changes in temperature.

* T.M. Wallis, J. Moreland and P. Kabos. 2006. Einstein-de Haas effect in a NiFe film deposited on a microcantilever. Applied Physics Letters. Sept. 18.