The magnetization of active elements in magnetic data storage devices is controlled by magnetic fields. Recently, spin currents are also being considered as an alternative means of changing the direction of the magnetization.

A much more efficient way would be the use of an external electric field to control the magnetization. Now, a team of scientists in Japan1 have achieved this in a magnetic semiconductor.

Fig. 1: Scheme of the structure used to demonstrate manipulation of the magnetization by an electric field. By applying a gate voltage – and therefore an electric field – between the magnetic semiconductor film and a metal gate the the direction of the magnetization can rotate in the plane of the film.

Hideo Ohno and colleagues based their experiment on the fact that the direction in which the magnetization lies in thin films of GaMnAs depends strongly on the concentration of holes (positive charges) in the film, and that this can be changed by the application of an electric field through an external gate (Fig. 1).

As a first step, the team determined the dependence of the orientation of the magnetization in the plane of the film, by linking it to the dependence of the Hall resistivity measured as a function of the orientation of a magnetic field. They found that by varying the gate voltage, the magnetization orientation for zero applied magnetic field could be varied by more than 10 degrees when the gave voltage varied between -12 and 12 V.

Next the researchers studied the variation of the magnetization component perpendicular to the film plane. Again, they verified that a gate voltage could be used to change the orientation of the magnetization with respect to the film plane if the magnetic field in the perpendicular direction was lower than a limiting value—at which point the magnetization simply oriented itself perpendicularly to the plane.

For Ohno and colleagues, not only manipulating but switching the direction of magnetization to other stable state is possible for a given set of conditions. “This opens up an entirely new route to the electrical switching of a magnet, which may lead to new nonvolatile memory and logic devices. We also believe that the electric-field manipulation becomes a viable means for metallic structures when the size is reduced to nanoscale,” says Ohno.