Topological insulator helps flip magnetisation in memory
Topological insulators may soon serve a practical purpose in controlling magnetic memory and logic devices as a team of researchers from Cornell and Penn State University has demonstrated that the electrical currents flowing along the surface of topological insulators can exert a torque on an adjacent magnetic layer that is 10 times more efficient than any other known mechanism.
This breakthrough provides a new strategy for making next-generation memory technologies that use the least possible energy and current. Led by Dan Ralph, the F.R. Newman Professor of Physics at Cornell, and Nitin Samarth of Penn State, the team used the topological insulator bismuth selenide for their experiments.
Like conventional insulators, topological insulators do not allow current to flow through the material, but they are different because they are wrapped in a conducting surface. Electrons flowing on the surface also do something unique: The direction of an electron's spin is always locked perpendicular to its direction of motion. This locking provides a means for the flow of an electrical current along the surface to produce a build-up of spin that can apply torque to an adjacent magnet.
Ralph and colleagues, in trying to develop magnetic nonvolatile memory and logic devices, identified finding a way to quickly flip the devices' magnetisation using the least possible current as one bottleneck. The results showed that electrical current flowing within a thin film of bismuth selenide – at room temperature no less – can be used for this purpose.
The researchers caution that actual memory devices are a long way off, but Ralph noted that it can be viewed as an exciting first step for a new branch of science. The collaborative Cornell and Penn State work is supported by a grant from DARPA (the Defense Advanced Research Projects Agency).