Yttrium Iron Garnet Waveguide Research Articles

A spin-wave frequency demultiplexer based on YIG nanowaveguides intersecting at a small angle

We experimentally demonstrate a simple design for a spin-wave frequency demultiplexer based on submicrometer-width yttrium iron garnet waveguides intersecting at an angle of 30°. We show that, depending on the frequency, spin waves excited in the input arm of the device are predominantly directed to one of the two output arms. This spin-wave routing is characterized by a large extinction ratio of about 10. The frequency response of the demultiplexer can be efficiently controlled by changing the static magnetic field and the geometry of the device. Due to the small intersection angle and symmetry of the device, its operation does not require conversion between different types of spin-wave modes. This results in a high efficiency of the device and allows its facile integration into magnonic networks for complex signal processing and computing with spin waves.

Nonreciprocal magnonic directional coupler based on metal-coated YIG adjacent stripes

Unidirectional information transport is often realized in magnonic application using the filters, isolators, and circulators. In this Letter, we propose the simple design of the unidirectional magnonic coupler, which is realized as a laterally coupled yttrium–iron–garnet waveguide coated with a metal layer. We experimentally discover and numerically confirm that the proposed structure can exhibit unidirectional coupling, which can be easily controlled by the direction of the external magnetic field. At the same time, we show how the dynamic magnetization profile of the spin wave is varied with the change in the propagation direction to the opposite along the coupler. Brillouin light scattering reveals the variation of the spatial spin-wave profile, which is then used to extract the value of the coupling length. The experimental results are in good agreement with the results of the coupling length estimation from two methods: eingenmode analysis and Landau–Lifshits–Gilbert solution in parallel with the Maxwell equations. This opens up alternative ways to fabricate the non-reciprocal magnonic devices. In particular, we consider the operation of the unidirectional magnonic coupler as a multi-regime logic device.

Operation of a submicrometer waveguide cross as a spin-wave logic gate

In this experimental study, we explore the potential implementation of logic operations using the interference of propagating spin waves within a device composed of intersecting yttrium iron garnet waveguides with submicrometer width. Our investigation reveals the significant influence of finite-size effects on the performance of the microscopic devices. In particular, we observe that their efficiency depends on the wavelengths of the involved spin waves in relation to the size of the interference region and is reduced by multimode spin-wave propagation. These findings highlight crucial factors to be considered when designing magnonic nanodevices operating with short-wavelength spin waves, providing valuable insights for optimizing their performance in practical applications.

Controlling the Modes of Spin Wave Propagation in an Yttrium Iron Garnet Waveguide by Local Laser Heating

Controlling the Modes of Spin Wave Propagation in an Yttrium Iron Garnet Waveguide by Local Laser Heating

Propagation of Spin Waves in Intersecting Yttrium Iron Garnet Nanowaveguides

We study experimentally the propagation of spin waves in waveguide structures consisting of two submicrometer-width yttrium iron garnet waveguides intersecting at a right angle. We show that, despite the significant spatial variations of the internal static magnet field and the in-plane anisotropy of the dispersion characteristics, the incident spin wave can efficiently pass through the microscopic cross-shaped structure and be transmitted into all its arms. This process depends strongly on the frequency of the wave and the orientation of the static magnetic field. By varying these parameters, one can achieve a controllable uniform or preferential transmission of the wave into different arms of the cross. Our results create the basis for the implementation of nanoscale magnonic networks to be used for the realization of complex non-Boolean data-processing schemes, including neuromorphic computing.

Tuning of spin-wave transmission and mode conversion in microscopic YIG waveguides with magnonic crystals

We report experimental results on spin-wave propagation, transmission gap tuning, and mode conversion in straight, curved, and Y-shaped yttrium iron garnet waveguides with magnonic crystals made of submicrometer-wide airgrooves. We observe forbidden frequency gaps with sizes up to 200 MHz in straight waveguides and narrowing of the gaps in curved and Y-shaped waveguides. The spin-wave transmission signal is strongly suppressed inside the gaps and remains high at allowed frequencies for all waveguide types. Using super-Nyquist sampling magneto-optical Kerr effect microscopy, we image symmetric and asymmetric spin-wave interference patterns, the self-focusing of propagating spin waves, and interconversions between width modes with different quantization numbers.

Physical realization of complex dynamical pattern formation in magnetic active feedback rings

We report the clean experimental realization of cubic–quintic complex Ginzburg–Landau (CQCGL) physics in a single driven, damped system. Four numerically predicted categories of complex dynamical behavior and pattern formation are identified for bright and dark solitary waves propagating around an active magnetic thin film-based feedback ring: (1) periodic breathing; (2) complex recurrence; (3) spontaneous spatial shifting; and (4) intermittency. These nontransient, long lifetime behaviors are observed in self-generated spin wave envelopes circulating within a dispersive, nonlinear yttrium iron garnet waveguide. The waveguide is operated in a ring geometry in which the net losses are directly compensated for via linear amplification on each round trip (of the order of 100 ns). These behaviors exhibit periods ranging from tens to thousands of round trip times (of the order of μs) and are stable for 1000s of periods (of the order of ms). We present ten observations of these dynamical behaviors which span the experimentally accessible ranges of attractive cubic nonlinearity, dispersion, and external field strength that support the self-generation of backward volume spin waves in a four-wave-mixing dominant regime. Three-wave splitting is not explicitly forbidden and is treated as an additional source of nonlinear losses. All observed behaviors are robust over wide parameter regimes, making them promising for technological applications. We present ten experimental observations which span all categories of dynamical behavior previously theoretically predicted to be observable. This represents a complete experimental verification of the CQCGL equation as a model for the study of fundamental, complex nonlinear dynamics for driven, damped waves evolving in nonlinear, dispersive systems. The reported dynamical pattern formation of self-generated dark solitary waves in attractive nonlinearity without external sources or potentials, however, is entirely novel and is presented for both the periodic breather and complex recurrence behaviors.

Multifrequency Spin-Wave Propagation for Parallel Data Processing Using Microstructured Yttrium Iron Garnet Thin Films

Spin waves (SWs) have tremendous application potential in wave-based computation utilizing a broad frequency spectrum spanning from the gigahertz-to-terahertz ranges. Like optical and other electromagnetic waves, SWs also promise to usher in a new era of parallel data processing with low-power consumption without Joule heating. However, this potential is undermined by the lack of investigation on multichannel networking and operation on single chips under a uniform bias magnetic field. This study proposes a multifrequency SW propagation based on shape anisotropy in microstructured rectangular waveguides made of yttrium iron garnet (YIG). The width-dependent transmission properties of magnetostatic surface SWs in the YIG waveguides were experimentally demonstrated. We revealed that the smaller width of the waveguide results in lower SWs frequency due to the demagnetizing field along the width direction. Multifrequency SW propagation was demonstrated in a device where three waveguides with widths of 10, 20, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$100~\mu \text{m}$ </tex-math></inline-formula> were connected to the common antennas. SWs propagation with the frequencies of 1.98, 2.11, and 2.18 GHz have been transmitted under a uniform bias magnetic field. Furthermore, we investigated SWs transmission in a device where three waveguides with different widths were interconnected at their ends and under one side of the antenna. We observed that the interconnected waveguides result in a single resonant frequency with flat band transmission because the whole waveguide structure is considered a single magnetic body. The results presented here provide guidelines for complex networks in frequency-division multiplexing operation.

Spin wave interference detection via inverse spin Hall effect

In this Letter, we present experimental data that demonstrate a spin wave interference detection using an inverse spin Hall effect (ISHE). Two coherent spin waves are excited in a yttrium-iron garnet waveguide by continuous microwave signals. The initial phase difference between the spin waves is controlled by the external phase shifter. The ISHE voltage is detected at a distance of 2 and 4 mm away from the spin wave generating antennas by an attached Pt layer. Experimental data show ISHE voltage oscillation as a function of the phase difference between the two interfering spin waves. This experiment demonstrates an intriguing possibility of using ISHE in a spin wave logic circuit converting a spin wave phase into an electric signal.

Phase shifter and broadband XOR logic gate based on edge-mode–type spin wave in the waveguide

We demonstrate an edge-mode–type phase shifter based on spin-orbit torque (SOT), and propose a broadband XOR logic gate based on the proposed phase shifter. A short length of cobalt (Co) magnetic element is placed parallel to one side of the yttrium iron garnet (YIG) spin wave waveguide to construct an edge-mode–type phase shifter of spin waves. It is numerically demonstrated that the wave number of spin waves at one side of YIG waveguide decreases locally due to the introduction of Co element, which leads to the phase difference between the two edge modes in the YIG waveguide. The amount of shifted phase can be controlled by the length of the Co element and spin polarization current intensity. Finally, a broadband XOR logic gate based on the edge-mode–type phase shifter is realized by applying spin polarized current. The proposed edge-mode–type shifter and XOR logic gate provide a new methodology for the designing of magnonic logic gates.

Parametric Generation of Propagating Spin Waves in Ultrathin Yttrium Iron Garnet Waveguides

Herein, experimental demonstration of the parallel parametric generation of spin waves in a microscaled yttrium iron garnet waveguide with nanoscale thickness is presented. Using Brillouin light scattering microscopy, the parametric excitation of the first and second waveguide modes by a stripline microwave pumping source is observed. Micromagnetic simulations reveal the wave vector of the parametrically generated spin waves. Based on analytical calculations, which are in excellent agreement with experiments and simulations, it is proved that the spin‐wave radiation losses are the determinative term of the parametric instability threshold in this miniaturized system. The used method enables the direct excitation and amplification of nanometer spin waves dominated by exchange interactions. The presented results pave the way for integrated magnonics based on insulating nanomagnets.

Reflection-less width-modulated magnonic crystal

The interest in artificial magnetic media such as magnonic crystals increased substantially in recent years due to their potential applications in information processing at microwave frequencies. The main features of these crystals are the presence of band gaps in the spin-wave spectra, usually formed due to Bragg reflections of spin-waves on the artificially created periodic structures. Here, we study spin-wave propagation in longitudinally magnetized width- and thickness-modulated yttrium iron garnet waveguides by means of Brillouin light scattering and microwave spectroscopy techniques. It is found that the width modulated crystal does not manifest noticeable Bragg reflections, but still demonstrates a pronounced band gap in its transmission characteristic. The phenomenon can be explained by the destructive interference between different frequency-degenerated spin-wave modes excited by the crystal. Such a reflection-less crystal is promising for future design of multi-element magnonic devices.

Spin-wave frequency division multiplexing in an yttrium iron garnet microstripe magnetized by inhomogeneous field

Spin waves are promising candidates for information processing and transmission in a broad frequency range. In the realization of magnonic devices, the frequency related division of the spin waves is a critical function for parallel information processing. In this work, we demonstrate a proof-of-concept spin-wave frequency division multiplexing method by magnetizing a homogeneous magnetic microstripe with an inhomogeneous field. The symmetry breaking additional field is introduced by a Permalloy stripe simply placed in lateral proximity to an yttrium iron garnet waveguide. Spin waves with different frequencies can propagate independently, simultaneously, and separately in space along the shared waveguide. This work demonstrates one potential way for parallel information transmission and processing in magnonics.

Spin Waves in YIG-Based Networks: Logic and Signal Processing

An eight-port magnonic network was fabricated from 1 μm thick epitaxial yttrium iron garnet (YIG) film by the photolithography and ion-etching techniques. The network had a form of the 2 × 2 lattice of the 10 μm wide and 100 μm long YIG waveguides with inductive micro-antennas located at the ends and spaced by 90 μm. Effects of the spin waves (SW) propagation and interference in the network were studied experimentally and by micromagnetic simulation. It was shown that one can realize the constructive and destructive interference of the SW at the output transducers by changing the input signals phase. Possibilities to build logic gates and magnetic sensors based on the SW interference was demonstrated.

Three port logic gate using forward volume spin wave interference in a thin yttrium iron garnet film

We demonstrate a logic gate based on interference of forward volume spin waves (FVSWs) propagating in a 54 nm thick, 100 μm wide yttrium iron garnet waveguide grown epitaxially on a garnet substrate. Two FVSWs injected by coplanar waveguides were made to interfere constructively and destructively by varying their phase difference, showing an XNOR logic function. The reflected and resonant waves generated at the edges of the waveguide were suppressed using spin wave absorbers. The observed isolation ratio was 19 dB for a magnetic field of ~2.80 kOe ( = 223 kA m−1) applied perpendicular to the film. The wavelength and device length were ~8.9 μm and ~53 μm, respectively. Further, the interference state of the SWs was analyzed using three-dimensional radio frequency simulations.

Microwave magnon damping in YIG films at millikelvin temperatures

Magnon systems used in quantum devices require low damping if coherence is to be maintained. The ferrimagnetic electrical insulator yttrium iron garnet (YIG) has low magnon damping at room temperature and is a strong candidate to host microwave magnon excitations in future quantum devices. Monocrystalline YIG films are typically grown on gadolinium gallium garnet (GGG) substrates. In this work, comparative experiments made on YIG waveguides with and without GGG substrates indicate that the material plays a significant role in increasing the damping at low temperatures. Measurements reveal that damping due to temperature-peak processes is dominant above 1 K. Damping behavior that we show can be attributed to coupling to two-level fluctuators (TLFs) is observed below 1 K. Upon saturating the TLFs in the substrate-free YIG at 20 mK, linewidths of ∼1.4 MHz are achievable: lower than those measured at room temperature.

Spin Pinning and Spin-Wave Dispersion in Nanoscopic Ferromagnetic Waveguides

Spin waves are investigated in yttrium iron garnet waveguides with a thickness of 39nm and widths ranging down to 50nm, i.e., with an aspect ratio thickness over width approaching unity, using Brillouin light scattering spectroscopy. The experimental results are verified by a semianalytical 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 semianalytical theory allows for the calculation of spin-wave mode profiles and dispersion relations in nanostructures.

Indirect observation of phase conjugate magnons from non-degenerate four-wave mixing

A phase conjugate mirror utilising four-wave mixing in a magnetic system is experimentally realised for the first time. Indirect evidence of continuous-wave phase conjugation has been observed experimentally and is supported by simulations. The experiment utilises a pump-probe method to excite a four-wave mixing process. Two antennae are used to pump a region of a thin-film yttrium iron garnet waveguide with magnons of frequency f_{1} to create a spatio-temporally periodic potential. As the probe magnons of f_{mathrm {p}} impinge on the pumped region, a signal with frequency f_{mathrm {c}} = 2f_{1}-f_{mathrm {p}} is observed. The amplitude of the nonlinear signal was highly dependent on the applied magnetic field H. Width modes of the probe magnons and standing wave modes of the pump magnons were shown to affect the amplitude of the signal at f_{{rm c}}. Experimental data are compared with simulations and theory to suggest that f_{{rm c}} is a phase conjugate of f_{{rm p}}.

Demonstration of a robust magnonic spin wave interferometer

Magnonics is an emerging field dealing with ultralow power consumption logic circuits, in which the flow of spin waves, rather than electric charges, transmits and processes information. Waves, including spin waves, excel at encoding information via their phase using interference. This enables a number of inputs to be processed in one device, which offers the promise of multi-input multi-output logic gates. To realize such an integrated device, it is essential to demonstrate spin wave interferometers using spatially isotropic spin waves with high operational stability. However, spin wave reflection at the waveguide edge has previously limited the stability of interfering waves, precluding the use of isotropic spin waves, i.e., forward volume waves. Here, a spin wave absorber is demonstrated comprising a yttrium iron garnet waveguide partially covered by gold. This device is shown experimentally to be a robust spin wave interferometer using the forward volume mode, with a large ON/OFF isolation value of 13.7 dB even in magnetic fields over 30 Oe.

Spin waves in micro-structured yttrium iron garnet nanometer-thick films

We investigated the spin-wave propagation in a micro-structured yttrium iron garnet waveguide of 40 nm thickness. Utilizing spatially-resolved Brillouin light scattering microscopy, an exponential decay of the spin-wave amplitude of (10.06 ± 0.83) μm was observed. This leads to an estimated Gilbert damping constant of α=(8.79±0.73)×10−4, which is larger than damping values obtained through ferromagnetic resonance measurements in unstructured films. The theoretically calculated spatial interference of waveguide modes was compared to the spin-wave pattern observed experimentally by means of Brillouin light scattering spectroscopy.