Nonreciprocal Devices & Directional Couplers Based on Nanoscale Magnonic Waveguides
Short-wavelength exchange-dominated spin waves propagating in magnonic waveguides could be used in energy-efficient microwave signal processing. The use of nano-scale magnonic waveguides allows one not only to miniaturize the microwave signal processing devices, but also to employ novel physical effects that are pronounced only at the nano-scale. In particular, in ultrathin bilayers made of ferromagnetic metals and dielectrics there is an effect of voltage-controlled magnetic anisotropy (VCMA) which makes possible excitation and manipulation of spin waves by electric fields. This effect is rather strong and is linear in the electric field. Another interesting interface effect that can be used at nano-scale is the interfacial Dzyaloshinskii-Moriya interaction (IDMI), which, in particular, may result in the nonreciprocity of spin waves, propagating in a nano-scale magnonic waveguide.
In this presentation we show how the spin wave nonreciprocity induced by IDMI affects the excitation and amplification of spin waves by the parametric VCMA pumping. A proper selection of the operational frequency allows one to make the idler (contra-propagating) spin wave in a parametric amplifier evanescent, thus crating a strong nonreciprocity. This effect not only enhances the total efficiency of the parametric amplification, but also eliminates the spurious influence of the contra-propagating idler wave on the adjacent signal processing devices and suppresses noise generation. It is also shown, that the optimum characteristics of a parametric spin wave amplifier are achieved in the adiabatic regime, when the length of the region where parametric amplification takes place is larger than spin wave wavelength. In contrast, for the parametric excitation of nonreciprocal spin waves it is necessary to work in the non-adiabatic regime, when the pumping is strongly localized in the region that is much shorter than the spin wave wavelength.
It is also shown, that the dipolar interaction between the nano-scale magnonic waveguides can be used to transfer the spin wave energy between the waveguides. If the interacting waveguides are identical, the spin-wave energy is fully transferred from one waveguide to another after a certain spin wave propagation distance, that we will call a coupling length. The coupling length depends on the geometry of the waveguides, on the distance between them, and on the spin wave frequency. This effect makes possible to use the dipolarly-coupled magnonic waveguides as power splitters and frequency separators, and as magnonic cross-conduits. The dependence of the coupling length on the relative orientation of the static magnetizations in the interacting waveguides may be used for the development of reconfigurable signal processing devices and fast spin-wave switches.
|Nonreciprocal Devices and Directional Couplers Based on Nano-scale Magnonic Waveguides|
Tuesday, April 4, 2017, 4 p.m.–5 p.m. ET
Durham, NC, United States