Feb 15, 2011
Computing with spin waves at the nanoscale
Wave interference patterns can be used to transmit, store and process information. A new nanometre-scale source of spin waves – spin torque nano-oscllators (STNOs) – permits such processing on extremely small spatial scales at gigahertz frequencies in thin ferromagnetic films. Wave propagation delays are used to encode data, much like neuronal conduction delays in axon function in the brain.
Researchers at New York University (NYU) have proposed computing devices made of STNO arrays on ferromagnetic thin films. The arrays can direct spin-wave energy in diffusing wave packets. This energy in turn can be detected through resistance changes in other oscillators. A simple circuit can be used to detect activity and respond by generating more activity, to create complex interference patterns that execute a desired function, such as data storage or logic operations.
STNOs are point contacts to a ferromagnetic metallic magnetic multilayer thin film. Spin-polarized currents in the contact create spin waves in ferromagnetic thin films that oscillate at microwave frequencies (1 to 100 GHz). STNOs can frequency lock either to one another or to external microwave sources so that their interference patterns are stable. Constructive interference thus defines preferred propagating directions (as occurs with antennas) or preferred positions for the spin-wave excitations. By controlling the distance between contacts, their sizes, and their oscillation phases, one can set almost any desired pattern of spin-excitations.
Configuring future devices
Reporting their results in the journal Nanotechnology, the researchers demonstrate how to construct persistently reverberating structures that may serve as storage units, encoding information in the phase with respect to either other structures or reference signals. One can also create look-up tables by programming the reverberating structures with graded frequencies. One can thus implement a computing methodology known as Polychonous Wavefront Computation, a brain inspired and non-synchronous theoretical paradigm. This proposal opens the door to experimental studies as well as further theoretical work. For example, it would be particularly interesting to consider wave propagation in nanostructure magnetic media in which the wave propagation can be anisotropic.
About the author
The study is the result of collaborative research between the New York University Department of Physics and Courant Institute for Mathematical Sciences. Prof. A D Kent leads a research group with interests in the physics of magnetic nanostructures, nanomagnetic devices and magnetic information storage. Prof. F C Hoppesnteadt has published 11 books and edited two in various areas of mathematics and mathematical biology. Dr F Macià, a postdoctoral researcher at NYU with a Catalan Fellowship, has a BA in mathematics and in telecommunication engineering and a PhD in physics. He particularly enjoys problems requiring multidisciplinary approaches.