Hybrid magnonic spintronic system for tunable broadband signal filtering and microwave generation

Abstract

Non-conventional beyond-the-state-of-the-art signal processing schemes require parallelism, scalability, robustness and energy efficiency to meet the demands of complex data-driven applications. With further research, magnonic and spintronic circuits can potentially help to fulfill these requirements. We present an experimental proof-of-concept of a hybrid device that can employ broad deteriorated microwave signals to excite and detect low energy propagating spin waves (SWs). For this, we use the output signal of a spin-transfer torque nano-oscillator (STNO) and connect it to a RF filter based on a magnonic delay-line. The STNO serves as a tunable nano-scaled signal generator with a broad output linewidth. Its RF output is fed as input into the magnonic delay-line circuit. Tuning the magnetic field solely at the magnonic circuit, we demonstrate the capability to selectively filter a broad RF input, obtaining a spin-wave output signal with a much narrower linewidth. This allows to tune the frequency of the RF signal at the output simply by tuning the magnetic field. Our findings are a first step towards a versatile, energy-efficient and compact wave-based filter with high sensitivity. Such a device can use even low-power, degraded signals and convert them into tunable SW outputs, effectively reducing the need for charge-based signal processing.

Figures (5)

• Figure 1: Schematic of the circuit constituting the STNO layer. Dc current $I_{\mathrm{STNO}}$ is injected into the STNO via a bias-T, which in turn is used to direct back the RF signal generated by the STNO through an amplifier and onto a spectrum analyzer. The STNO is placed between the poles of an electric magnet that generates and in-plane magnetic field $B_{\mathrm{STNO}}$.
• Figure 2: (a) 2D color-plot of the frequency dependence of the STNO's output signal on the applied magnetic field $B_{\mathrm{STNO}}$ at $I_{\mathrm{STNO}}$ = [3]mA. The dotted black line represents the chosen field at which the STNO will be operated throughout the experiment. (b) Power spectrum of the STNO's microwave output at fixed $B_{\mathrm{STNO}}$ and $I_{\mathrm{STNO}}$.
• Figure 3: (a) Schematic of the magnonic circuit where Coplanar waveguide antennas are used to excite and detect spin waves. The magnetic field $B_{\mathrm{SW}}$ is applied perpendicular to the SW propagation direction. (b) The detected SW signal, as excited by the microwave signal generator, at the resonant Fields $B_{\mathrm{SW}}$.
• Figure 4: (a) Calculated spin wave dispersion curves for the utilized Yttrium-Iron-Garnet chip for fields ranging from [40]mT up to [89]mT. The antenna's excitation efficiency is shown on the right-hand side. Maximum efficiency lies around wave-vectors close to [0.7]rad/$\mu$m (b) Spectra of the forward transmission (component S$_{21}$ of the scattering matrix) as obtained from a vector network analyzer for fields ranging from [40]mT up to [98]mT. The black line traced at the base of the transmission spectra is the electromagnetic cross-talk between the two CPWs at zero field.
• Figure 5: (a) The proposed concept of the magnonic filter consisting of the source (STNO circuit) and the filtering device (SW circuit). (b) 2D color-plot of the frequency dependence of the SW's output signal on the applied magnetic field $B_{\mathrm{SW}}$ at fixed STNO conditions: $B_{\mathrm{SW}}$ = [21]mT and $I_{\mathrm{STNO}}$ = [3]mA. (c) Signals filtered by the SW layer for different $B_{\mathrm{SW}}$ values ranging from [43]mT to [70]mT in reference to the broad input signal from STNO (black curve).