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Register a new userSpin pinning and spin-wave dispersion in nanoscopic ferromagnetic waveguides
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Spin waves are investigated in Yttrium Iron Garnet (YIG) waveguides with a thickness of 39 nm and widths ranging down to 50 nm, i.e., with aspect ratios thickness over width approaching unity, using Brillouin Light Scattering spectroscopy. The experimental results are verified by a semi-analytical theory and micromagnetic simulations. A critical width is found, below which the exchange interaction suppresses the dipolar pinning phenomenon. This changes the quantization criterion for the spin-wave eigenmodes and results in a pronounced modification of the spin-wave characteristics. The presented semi-analytical theory allows for the calculation of spin-wave mode profiles and dispersion relations in nano-structures.
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The field of magnonics attracts significant attention due to the possibility of utilizing information coded into the spin-wave phase or amplitude to perform computation operations on the nanoscale. Recently, spin waves were investigated in Yttrium Iron Garnet (YIG) waveguides with widths ranging down to 50 nm and aspect ratios thickness over width approaching unity. A critical width was found, below which the exchange interaction suppresses the dipolar pinning phenomenon and the system becomes unpinned. Here we continue these investigations and analyse the pinning phenomenon and spin-wave dispersions as a function of temperature, thickness and material of choice. Higher order modes, the influence of a finite wavevector along the waveguide and the impact of the pinning phenomenon on the spin-wave lifetime are discussed as well as the influence of a trapezoidal cross section and edge roughness of the waveguides. The presented results are of particular interest for potential applications in magnonic devices and the incipient field of quantum magnonics at cryogenic temperatures.
Magnetostatic spin wave dispersion and loss are measured in micron scale spin wave-guides in ferromagnetic, metallic CoTaZr. Results are in good agreement with model calculations of spin wave dispersion. The measured attenuation lengths, of the order of 3um, are several of orders of magnitude shorter than that predicted from eddy currents in these thin wires. Spin waves effectively tunnel through air gaps, produced by focused ion beam etching, as large as 1.5 um.
By their very nature, voltage/current excited Spin Waves (SWs) propagate through waveguides without consuming noticeable power. If SW excitation is performed by the continuous application of voltages/currents to the input, which is usually the case, the overall energy consumption is determined by the transducer power and the circuit critical path delay, which leads to high energy consumption because of SWs slowness. However, if transducers are operated in pulses the energy becomes circuit delay independent and it is mainly determined by the transducer power and delay, thus pulse operation should be targeted. In this paper, we utilize a 3-input Majority gate (MAJ) to investigate the Continuous Mode Operation (CMO), and Pulse Mode Operation (PMO). Moreover, we validate CMO and PMO 3-input Majority gate by means of micromagnetic simulations. Furthermore, we evaluate and compare the CMO and PMO Majority gate implementations in term of energy. The results indicate that PMO diminishes MAJ gate energy consumption by a factor of 18. In addition, we describe how PMO can open the road towards the utilization of the Wave Pipelining (WP) concept in SW circuits. We validate the WP concept by means of micromagnetic simulations and we evaluate its implications in term of throughput. Our evaluation indicates that for a circuit formed by four cascaded MAJ gates WP increases the throughput by 3.6x.
Magnonics is seen nowadays as a candidate technology for energy-efficient data processing in classical and quantum systems. Pronounced nonlinearity, anisotropy of dispersion relations and phase degree of freedom of spin waves require advanced methodology for probing spin waves at room as well as at mK temperatures. Yet, the use of the established optical techniques like Brillouin light scattering (BLS) or magneto optical Kerr effect (MOKE) at ultra-low temperatures is forbiddingly complicated. By contrast, microwave spectroscopy can be used at all temperatures but is usually lacking spatial and wavenumber resolution. Here, we develop a variable-gap propagating spin-wave spectroscopy (VG-PSWS) method for the deduction of the dispersion relation of spin waves in wide frequency and wavenumber range. The method is based on the phase-resolved analysis of the spin-wave transmission between two antennas with variable spacing, in conjunction with theoretical data treatment. We validate the method for the in-plane magnetized CoFeB and YIG thin films in $kperp B$ and $kparallel B$ geometries by deducing the full set of material and spin-wave parameters, including spin-wave dispersion, hybridization of the fundamental mode with the higher-order perpendicular standing spin-wave modes and surface spin pinning. The compatibility of microwaves with low temperatures makes this approach attractive for cryogenic magnonics at the nanoscale.
Spin-wave propagation in an assembly of microfabricated 20 nm thick, 2.5 {mu}m wide Yttrium Iron Garnet (YIG) waveguides is studied using propagating spin-wave spectroscopy (PSWS) and phase resolved micro-focused Brillouin Light Scattering ({mu}-BLS) spectroscopy. We show that spin-wave propagation in 50 parallel waveguides is robust against microfabrication induced imperfections. Spin-wave propagation parameters are studied in a wide range of excitation frequencies for the Damon-Eshbach (DE) configuration. As expected from its low damping, YIG allows the propagation of spin waves over long distances (the attenuation lengths is 25 {mu}m at mu$_{0}$H = 45 mT). Direct mapping of spin waves by {mu}-BLS allows us to reconstruct the spin-wave dispersion relation and to confirm the multi-mode propagation in the waveguides, glimpsed by propagating spin-wave spectroscopy.
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