Credit: © 2008 Nature Materials

Materials that exhibit both ferroelectricity and ferromagnetism could have applications in data storage and spintronics. However, despite significant advances in our understanding of the physical properties of these multiferroic materials, difficulties in combining them with semiconductor electronics is limiting their applications. Now, Igor Stolichnov of the EPFL in Lausanne and co-workers from Europe and New Zealand have shown that ferromagnetism in (Ga,Mn)As — a well known magnetic semiconductor — can be controlled by applying voltages to a ferroelectric gate electrode1.

The group's devices consisted of a 7-nm-thick conducting channel made of (Ga,Mn)As and a 200-nm-thick gate made of a copolymer (polyvinylidene fluoride with trifluoroethylene). The combination of a magnetic semiconductor and a copolymer — which produced good polarization characteristics when annealed at the relatively low temperature of 140°C — was critical to the success of the devices.

Applying a voltage to the polymer gate changed its polarization state, which in turn changed the Curie temperature — the temperature above which a ferromagnetic material is no longer ferromagnetic — of the (Ga,Mn)As channel. These results could lead to the development of ferroelectric-gate field-effect transistor devices.