Reconfigurable dynamic states in Heusler based magnonic crystals

Abstract

Spin waves are promising to develop post-CMOS and/or green technologies due to their sub-micron wavelengths in the GHz range, their frequency tuning with magnetic or electric fields and their small energy dissipation during propagation. Many spin waves based applications have already been demonstrated for data processing and other microwave devices (filters, resonators, delay lines…).To reach these objectives, magnonic crystals (MC) consisting of a periodic modulation of magnetic properties are among the most promising geometries. One key point for applications with MC is to remove the static bias field as most devices operate at zero field. So technological developments imply to find solutions to obtain well-defined spin waves modes at remanence, with the possibility to modify purposely the spin wave spectrum to achieve different functionalities. While several approaches for reconfigurable states have been proposed [1-4], a “material approach” consisting in exploiting the crystal anisotropy of magnetic materials has been poorly explored up to now.Here we show by micromagnetic simulations that materials such as Co2MnSi Heusler alloy with strong cubic anisotropy can be used to obtain very different spin waves modes at remanence in a simple and classical geometry (Fig. 1 and Fig. 2). In particular, we demonstrate the variation of remanent configuration after saturation with a weak external field H0 (< 50 Oe) in different directions. This allows to decrease the amplitude, extinct or shift the frequencies of the different modes depending if they correspond to edge or volume modes. We will show the advantage of using cubic anisotropy with respect to isotropic material by comparing the amplitude variation of the different modes. Finally, we will also show that proper design of the crystal with respect to the cubic anisotropy directions can achieve a microwave response very robust against magnetic perturbation.  Fig. 1: Remanent magnetic states for different H0 directions.The dot edge size is 300 nm and the spacing is 900 nm.  Fig. 2: Corresponding FFT spectrum for a RF field along x. The calculated spatial profiles of the spin waves modes at particular frequencies are shown for the configuration A.