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How to Produce Unidirectional Spin Waves

Researchers from INAC have modeled spin wave sources using base metals. They showed that the presence of the interaction called Dzyaloshinskii-Moriya in these materials, combined with a judicious choice of system geometry, allows for the obtaining of a spin wave source that is unidirectional.
Published on 6 June 2017

In an ordinary planar waveguide, such as the one the scientists have modeled, spin waves travel indifferently in both directions.

Opting for a guide formed by a stack [(nickel-iron) alloy – platinum] on silicon permits the use of a specific interaction present at the alloy-platinum interface. This Dzyaloshinskii-Moriya interaction has the effect of shifting the frequency spectra of the waves propagating along the two opposite directions. Cleverly selecting the spatial excitation frequency then makes it possible to select only one way of propagation, while "turning off" the other.

This can be achieved by producing the spin wave by means of a second metallic guide that is perpendicular to the first and whose comb-like shape makes it possible to select the wave excitation vector, and consequently, the spin wave spatial period.

Spin waves could increase the efficiency of logical architectures (which currently rely upon CMOS devices) by allowing an undulatory logic at nanometric scale. They can, in fact, transfer information that is encoded in its amplitude and/or its phase. Additionally, their nanometric wavelength at frequencies in the gigahertz-terahertz range, as well as their integrability on a chip and their compatibility with non-volatile magnetic memories, makes them particularly competitive (compared to photonics, for instance).

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