Electric Field Enables Magnetic Semi Reversals
The field effect experiments were performed on the ferromagnetic semiconductor manganese-doped indium arsenide (In,Mn)As. The material was incorporated as the channel layer in a metal-insulator-semiconductor field effect transistor (FET). By changing the sign of the electric field of 1.5MV/cm, the magnetic field required to reverse the material's magnetisation at 40K changed by a factor of five (from 1.0mT to 0.2mT).
Such studies could find application in magnetic memory. To achieve nanoscale bits, the magnetic energy density of the material has to be increase to ensure stability against thermal fluctuation. However, a high magnetic energy density increases the magnetic field needed to reverse the magnetisation. Applying an electric field could reduce the magnetic field needed to write data.
Raising such possibilities to room temperature (around 300K) is a major challenge. Ferromagnetism in thin-film semiconductors has been seen up to 60K for (In,Mn)As and up to 160K in (Ga,Mn)As. Theoretical considerations suggest that room temperature ferromagnetism could be reached by increasing Mn concentrations by a factor of two for (Ga,Mn)As and a factor of five for (In,Mn)As. Such concentrations have not been realised experimentally due to defects and the formation of an MnAs phase that reduces Mn concentrations in the host.