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Magnonic Holographic Read-Only Memory
Abstract
In this work, we consider the possibility of building magnonic holographic read-only memory (MH-ROM) devices exploiting spin-wave interference for readout. MH-ROM consists of a grid of magnetic waveguides connected via cross junctions. Some of the cross junctions have a hole in the center of junctions, whereas others do not. The presence/absence of the hole is assigned to the memory states 0 and 1, respectively. We present experimental data showing spin-wave propagation modification in the Permalloy cross junction due to the presence of the hole. The results show prominent spin-wave modulation which is applicable for application in MH-ROM. Similar to the optical compact-disk ROM (CD-ROM), the internal memory states can be recognized via spin-wave interference. The advantages of using of spin waves instead of optical beams are scalability and compatibility with conventional electronic devices. The memory density scales inversely proportional to the operational wavelength. According to the estimates, the memory density of MH-ROM can be 1 Tb/cm(2) at wavelength lambda = 100 nm. We discuss the physical limitations and physical constrains associated with the spin-wave interference. The development of MH-ROMs opens a new horizon for building scalable holographic devices compatible with conventional electronic devices.
... Moreover, solutions known from photonics, spintronics and electronics can be applied also on ground of the magnonics. Furthermore, taking use of SWs as an information carrier gives possibility to exploit also non-Boolean wave-computing [12], holographic memory [11,13] or physically realized neural networks [14]. In these approaches crucial is not only SWs amplitude manipulation but also their phase. ...
... In these approaches crucial is not only SWs amplitude manipulation but also their phase. In magnonic it can be realized by magnonic crystals or by SWs scattering on some disturbances, like holes [13], domain walls [15] or magnetic elements placed on waveguides cross junctions [11]. However, in modern photonics also another approach have emerged, which exploit socalled metasurfaces, which enable electromagnetic waves manipulation at subwavelenght distances [16]. ...
... [45] In the case of two the same extended materials with zero anisotropy (K 1 = K 2 = 0) the GH shifts for reflected and refracted SWs are equal to each other ∆ t = ∆ r . This is because there are the same expressions for the phase shifts ϕ r and ϕ t [see, Eqs (12) and (13)] in this case. From these equations it also comes out that the GH shift dependence on the magnetic anisotropy at the interface is antisymmetric function of the K 12 , it takes positive (negative) values of the shift for K 12 < 0 (K 12 > 0) (see Fig. 4(b)). ...
Spin waves (SWs), the main object of investigation in magnonics, are promising information carriers. Nowadays, the most popular approach is a consideration of plane-wave-like SWs or SWs propagating in confined structures, like waveguides. Here, we study oblique incidence of SWs Gaussian beam at the interface between two identical ferromagnetic materials separated by a ultra-narrow interface. With the use of the analytical model and micromagnetic simulations we provide deep analysis of an influence of the interface properties, in particular magnetic anisotropy, on a transmission of the SW beam. We have obtained analytical formula for the reflectance and transmittance, phase shifts and a value of the Goos-Hänchen (GH) shift for reflected, and for the first time, refracted beams at the interface between two semi-infinite ferromagnetic media. Existence of the GH shift in reflection and transmission of the SW beams are confirmed with micromagnetic simulations for the thin film geometry. We demonstrated influence of the magnetic anisotropy at the interface, angle of incidence and frequency of SWs on the aforementioned properties. Additionally, we have developed method of high quality SW beam excitation suitable for micromagnetic simulations.
... The read-out time can be minimized by the scaling down of magnonic mesh size. There are no physical constraints for scaling down the size of the magnets to the tens of nanometers 24 . It may be possible to place a 1000 × 1000 micro-magnet array on the 10 × 10 mm ferrite film. ...
In this work, we consider a type of magnetic memory where information is encoded into the mutual arrangement of magnets. The device is an active ring circuit comprising magnetic and electric parts connected in series. The electric part includes a broadband amplifier, phase shifters, and attenuators. The magnetic part is a mesh of magnonic waveguides with magnets placed on the waveguide junctions. There are amplitude and phase conditions for auto-oscillations to occur in the active ring circuit. The frequency(s) of the auto-oscillation and spin wave propagation path(s) in the magnetic part depends on the mutual arrangement of magnets in the mesh. The propagation path is detected with a set of power sensors. The correlation between circuit parameters and spin wave path is the basis of memory operation. The combination of input/output switches connecting electric and magnetic parts and electric phase shifters constitute the memory address. The output of the power sensors is the memory state. We present experimental data on the proof-of-the-concept experiments on the prototype with three magnets placed on top of a single-crystal yttrium iron garnet Y 3 Fe 2 (FeO 4 ) 3 (YIG) film. There are three selected places for the magnets to be placed. There is a variety of spin wave propagation paths for each configuration of magnets. The results demonstrate a robust operation with an On/Off ratio for path detection exceeding 35 dB at room temperature. The number of possible magnet arrangements scales factorially with the size of the magnetic part. The number of possible paths per one configuration scales factorial as well. It makes it possible to drastically increase the data storage density compared to conventional memory devices. Magnonic combinatorial memory with an array of 100 × 100 magnets can store all information generated by humankind. Physical limits and constraints are also discussed.
... Apart from its potential, the HDS systems must solve many challenges before enterprises can commercialize HDS devices. The main challenges, in terms of signal processing, can be named as misalignment, inter-page interference (IPI), blur effect, and two-dimensional (2D) interference (Gertz et al., 2015(Gertz et al., , 2016Katano et al., 2017;Nguyen & Lee, 2015b). Intersymbol interference (ISI) is inherent in high-density storage systems, and the effect becomes significant in 2D storage systems. ...
This paper presents a 4/5 4-ary modulation code design for 4-level holographic data storage (HDS) systems. The multi-level HDS systems, capable of far greater storage densities than traditional storage technologies, are regarded as one of the most promising candidates for ultra-high-capacity optical storage devices. Significantly, the HDS systems promises to provide the best solutions for cloud storage services. Yet, the systems are significantly disturbed by many challenges, such as two-dimensional (2D) interference, blur effect, and misalignment. The proposed code is designed based on a 4-step procedure, where the codewords at the output of the encoder can avoid not only the effect of the worst 2D interference but also obtain a minimum distance between two arbitrary codewords of 0.47, which is larger than the minimum distance of a conventional 6/9 modulation code. Simulation results demonstrate that the proposal gains about 1 dB better than the traditional 6/9 modulation code at a ${10^{ - 9}}$10−9 bit error rate.
... In MHM, memory states are associated with the magnetization state of a magnet (e.g., presence/absence of a magnet) on top of a spin wave bus. 6,12 The interaction between the magnetic bits and propagating spin waves is the base of MHM operation. In our preceding work, 13 we presented experimental data showing the change of spin wave transmitted and reflected signals depending on the micro magnet position on yttrium iron garnet (YIG) film. ...
Magnonic holographic memory is a type of memory that uses spin waves for magnetic bit read-in and read-out. Its operation is based on the interaction between magnets and propagating spin waves where the phase and the amplitude of the spin wave are sensitive to the magnetic field produced by the magnet. Memory states 0 and 1 are associated with the presence/absence of the magnet in a specific location. In this work, we present experimental data showing the feasibility of magnetic bit location using spin waves. The testbed consists of four micro-antennas covered by Y 3 Fe 2 (FeO 4 ) 3 yttrium iron garnet (YIG) film. A constant in-plane bias magnetic field is provided by NdFeB permanent magnet. The magnetic bit is made of strips of magnetic steel to maximize interaction with propagating spin waves. In the first set of experiments, the position of the bit was concluded by the change produced in the transmittance between two antennas. The minima appear at different frequencies and show different depths for different positions of the bit. In the second set of experiments, two input spin waves were generated, where the phase difference between the waves is controlled by the phase shifter. The minima in the transmitted spectra appear at different phases for different positions of magnetic bit. The utilization of the structured bit enhances its interaction with propagating spin waves and improves recognition fidelity compared to a regular-shaped bit. The recognition accuracy is further improved by exploiting spin wave interference. The depth of the transmission minima corresponding to different magnet positions may exceed 30 dB. All experiments are accomplished at room temperature. Overall, the presented data demonstrate the practical feasibility of using spin waves for magnetic bit red-out. The practical challenges are also discussed.
... We believe that our results are of potential interest in realizing magnonic pass-band and stop-band filters which could be used for SW geometrical optics, 10,11 magnetic microparticle imaging, 47 non-Boolean computing 48 and for magnonic holographic read-only memory. 49 It is worth noting that the used approach for calculation of the focusing transducer can be applied for the calculation for SW lenses in the form of shaped thickness steps in magnetic films. 17,37 Indeed, in accordance with Huygens' principle, the SW's secondary sources on the wave front will define SW behavior in the following time. ...
The focusing effect for spin waves excited by a curved micrometer-sized coplanar waveguide transducer on top of a 5-μm-thick epitaxial yttrium iron garnet film is studied by means of the micro-focused Mandelstam-Brillouin light scattering technique and micromagnetic simulations. The curvilinear transducer is designed to focus the backward volume spin waves on the in-plane bias magnetic field applied along the symmetry axis of the transducer. We show that two-dimensional maps of spin wave intensity exhibit nonreciprocal properties without mirror symmetry with respect to the magnetic field direction and the focusing effect. The observed effects are the consequence of nonreciprocity of the backward volume spin waves travelling at an angle toward the bias field direction.
By their very nature, Spin Waves (SWs) excited at the same frequency but different amplitudes, propagate through waveguides and interfere with each other at the expense of ultra-low energy consumption. In addition, all (part) of the SW energy can be moved from one waveguide to another by means of coupling effects. In this paper we make use of these SW features and introduce a novel non Boolean algebra based paradigm, which enables domain conversion free ultra-low energy consumption SW based computing. Subsequently, we leverage this computing paradigm by designing a non-binary spin wave adder, which we validate by means of micro-magnetic simulation. To get more inside on the proposed adder potential we assume a 2-bit adder implementation as discussion vehicle, evaluate its area, delay, and energy consumption, and compare it with conventional SW and 7 nm CMOS counterparts. The results indicate that our proposal diminishes the energy consumption by a factor of
$3.14 \times $
and
$6 \times $
, when compared with the conventional SW and 7 nm CMOS functionally equivalent designs, respectively. Furthermore, the proposed non-binary adder implementation requires the least number of devices, which indicates its potential for small chip real-estate realizations.
In this work, we present experimental data demonstrating the possibility of
using magnonic holographic devices for pattern recognition. The prototype
eight-terminal device consists of a magnetic matrix with micro-antennas placed
on the periphery of the matrix to excite and detect spin waves. The principle
of operation is based on the effect of spin wave interference, which is similar
to the operation of optical holographic devices. Input information is encoded
in the phases of the spin waves generated on the several edges of the magnonic
matrix, while the output corresponds to the amplitude of the inductive voltage
produced by the interfering spin waves on the other side of the matrix. The
level of the output voltage depends on the combination of the input phases as
well as on the internal structure of the magnonic matrix. Experimental data
collected for several magnonic matrixes show the unique output signatures in
which maxima and minima correspond to specific input phase patterns.
Potentially, magnonic holographic devices may provide a higher storage density
compare to the optical counterparts due to a shorter wavelength and
compatibility with conventional electronic devices. The challenges and
shortcoming of the magnonic holographic devices are also discussed.
In this work, we present recent developments in magnonic holographic memory
devices exploiting spin waves for information transfer. The devices comprise a
magnetic matrix and spin wave generating/detecting elements placed on the edges
of the waveguides. The matrix consists of a grid of magnetic waveguides
connected via cross junctions. Magnetic memory elements are incorporated within
the junction while the read-in and read-out is accomplished by the spin waves
propagating through the waveguides. We present experimental data on spin wave
propagation through NiFe and YIG magnetic crosses. The obtained experimental
data show prominent spin wave signal modulation (up to 20 dB for NiFe and 35 dB
for YIG) by the external magnetic field, where both the strength and the
direction of the magnetic field define the transport between the cross arms. We
also present experimental data on the 2-bit magnonic holographic memory built
on the double cross YIG structure with micro-magnets placed on the top of each
cross. It appears possible to recognize the state of each magnet via the
interference pattern produced by the spin waves with all experiments done at
room temperature. Magnonic holographic devices aim to combine the advantages of
magnetic data storage with wave-based information transfer. We present
estimates on the spin wave holographic devices performance, including power
consumption and functional throughput. According to the estimates, magnonic
holographic devices may provide data processing rates higher than 10^18
bits/cm2/s while consuming 0.15uW. Technological challenges and fundamental
physical limits of this approach are also discussed.
In this work, we report on the demonstration of voltage-driven spin wave excitation, where spin waves are generated by multiferroic magnetoelectric (ME) cell transducers driven by an alternating voltage, rather than an electric current. A multiferroic element consisting of a magnetostrictive Ni film and a piezoelectric [Pb(Mg1/3Nb2/3)O3](1−x)–[PbTiO3]x substrate was used for this purpose. By applying an AC voltage to the piezoelectric, an oscillating electric field is created within the piezoelectric material, which results in an alternating strain-induced magnetic anisotropy in the magnetostrictive Ni layer. The resulting anisotropy-driven magnetization oscillations propagate in the form of spin waves along a 5 μm wide Ni/NiFe waveguide. Control experiments confirm the strain-mediated origin of the spin wave excitation. The voltage-driven spin wave excitation, demonstrated in this work, can potentially be used for low-dissipation spin wave-based logic and memory elements.
Early experiments in magnonics were made using ferrite samples, largely due to the intrinsically low magnetic (spin-wave) damping in these materials. Historically, magnonic phenomena were studied on micrometre to millimetre length scales. Today, the principal challenge in applied magnonics is to create sub-micrometre devices using modern polycrystalline magnetic alloys. However, until certain technical obstacles are overcome in these materials, ferrites—in particular yttrium iron garnet (YIG)—remain a valuable source of insight. At a time when interest in magnonic systems is particularly strong, it is both useful and timely to review the main scientific results of YIG magnonics of the last two decades, and to discuss the transferability of the concepts and ideas learned in ferrite materials to modern nano-scale systems.
The propagating spin wave spectroscopy (PSWS) technique is applied
for the first time to metallic thin film patterns, allowing to
measure their magnetostatic wave modes. Using micrometer scale
local excitation and detection, we show that magnetostatic
surface waves propagate on a distance as long as 40 μm
in a continuous permalloy film. In micrometer wide permalloy
stripes, we observe both quantized spin wave modes and
quasi-saturation modes, well explained by existing models. In
addition, low-frequency additional modes were observed which, we
suggest, are generated in the magnetically inhomogeneous edge
regions.
Problem of the propagation of spin waves in a one-dimensional magnonic crystal with a structure defect has been analyzed theoretically.
As a magnonic crystal, we consider a multilayer magnet representing an infinite system of plane-parallel alternate adjacent
exchange-coupled slabs of magnets of two types. As a single structure defect that breaks the translational symmetry of the
crystal, we consider a layer that is different from the layers composing the magnonic crystal. A dispersion law for spin-wave
modes localized at the defect has been obtained. The appearance of several defect modes in the band gap has been analyzed
depending on the parameters of the defect layer.
Spin torque oscillators with nanoscale electrical contacts are able to produce coherent spin waves in extended magnetic films, and offer an attractive combination of electrical and magnetic field control, broadband operation, fast spin-wave frequency modulation, and the possibility of synchronizing multiple spin-wave injection sites. However, many potential applications rely on propagating (as opposed to localized) spin waves, and direct evidence for propagation has been lacking. Here, we directly observe a propagating spin wave launched from a spin torque oscillator with a nanoscale electrical contact into an extended Permalloy (nickel iron) film through the spin transfer torque effect. The data, obtained by wave-vector-resolved micro-focused Brillouin light scattering, show that spin waves with tunable frequencies can propagate for several micrometres. Micromagnetic simulations provide the theoretical support to quantitatively reproduce the results.
The spin torque effect that occurs in nanometre-scale magnetic multilayer devices can be used to generate steady-state microwave signals in response to a d.c. electrical current. This establishes a new functionality for magneto-electronic structures that are more commonly used as magnetic field sensors and magnetic memory elements. The microwave power emitted from a single spin torque nano-oscillator (STNO) is at present typically less than 1 nW. To achieve a more useful power level (on the order of microwatts), a device could consist of an array of phase coherent STNOs, in a manner analogous to arrays of Josephson junctions and larger semiconductor oscillators. Here we show that two STNOs in close proximity mutually phase-lock-that is, they synchronize, which is a general tendency of interacting nonlinear oscillator systems. The phase-locked state is distinct, characterized by a sudden narrowing of signal linewidth and an increase in power due to the coherence of the individual oscillators. Arrays of phase-locked STNOs could be used as nanometre-scale reference oscillators. Furthermore, phase control of array elements (phased array) could lead to nanometre-scale directional transmitters and receivers for wireless communications.
Holography is a technique based on the wave nature of light which allows us
to utilize wave interference between the object beam and the coherent
background. Holography is usually associated with images being made from light,
however, this is only a narrow field of holography. The first holograms were
designed for use with electron microscopes and it was not until a decade later
with the advent of the laser that optical holographic images were popularized.
Multiple other fields have had major contributions made by using wave
interference to produce holograms, including acoustic holograms used in seismic
applications, and microwave holography used in radar systems. Holography has
been also recognized as a future data storing technology with unprecedented
data storage capacity and ability to write and read a large number of data in a
highly parallel manner. Here, we present a magnonic holographic memory device
exploiting spin wave interference.
In this work, we consider the possibility of building magnetic analog logic devices utilizing spin wave interference for special task data processing. As an example, we consider a multi-terminal magnonic matrix switch comprising multiferroic elements and a two-dimensional grid of magnetic waveguides connected via four-terminal cross-junctions. The multiferroic elements are placed on the periphery of the switch and used as input/output ports for signal conversion among the electric and magnetic domains. Data processing is accomplished via the use of spin wave interference within the magnonic matrix. We present the results of numerical modeling illustrating device operation for pattern matching, finding the period of the data string, and image processing. We also present the results of numerical modeling showing the device capabilities as a magnetic holographic memory. Magnonic holographic devices are of great potential to complement the conventional general-type processors in special task data processing and may provide a new direction for functional throughput enhancement. According to estimates, magnonic holographic devices can provide up to 1 Tb/cm2 data storage density and data processing rate exceeding 1018 bits/s/cm2. The physical limitations and practical challenges of the proposed approach are discussed.
We have used micromagnetic simulations to demonstrate a method for controlling the amplitude and phase of spin waves propagating inside a magnonic waveguide. The method employs a nanomagnet formed on top of a magnonic waveguide. The function of the proposed device is controlled by defining the static magnetization direction of the nanomagnet. The result is a valve or phase shifter for spin waves, acting as the carrier of information for computation or data processing within the emerging spin wave logic architectures of magnonics. The proposed concept offers such technically important benefits as energy efficiency, non-volatility, and miniaturization.
A discussion is given of the dispersion relation, magnetization distribution, and group velocity of magnetostatic waves in an infinite circular cylinder with the static magnetic field parallel to the cylinder axis. The dispersion relation of the modes with eivarphi angular dependence is, for kR>>1, omega≅gammaH0+gamma2piMs(xikR)2+(Dℏ)k2, where xi is a root of J0(x)=0; R is the cylinder radius; and D is the exchange constant. The group velocity of magnetostatic pulses at low wave vectors is shown to be considerably higher than magnon velocities.
Propagation of spin waves (SWs) through a periodic multilayered magnetic structure is analyzed. It is assumed that the structure consists of ferromagnetic layers having the same thickness but different magnetizations. The wave spectrum obtained contains forbidden zones (stop bands) in which wave propagation is prohibited. Introduction into the structure of the ferromagnetic layer with a different thickness breaks the structural symmetry and leads to a localization of the SW mode with the frequency lying in the stop band. Reflection of the wave by the structure of the finite length and transmission of the wave through the structure are also investigated. Numerical calculations of the wave dispersion and the transmission coefficients for symmetrical periodic structures as well as the structures with a defect are presented. Drawing an analogy from photonic crystals known in optics, such magnetic structures can be called one-dimensional (1-D) magnonic crystals (MCs). The possibilities of existence of the 2-D MCs are also discussed.
The most successful use of optical memories so far has been as read-only memories (ROM). A main reason for this success has been the availability of inexpensive methods to mass-produce copies of recorded disks. This has made it possible to publish data (audio, video, databases, computer games) and distribute it widely through normal retail channels. In this chapter, we show results of a holographic read-only memory (HROM) of which digital data on a master disk can be copied onto replicate disks efficiently.
We measure the propagation of spatially localized spin waves in NiFe thin films through local inductive detection of the dynamic magnetization. A pulsed magnetic field excites a linear superposition of spin wave modes with a distribution that is predominantly driven by the spatial dependence of the in-plane excitation field. The results of numerical micromagnetic calculations exhibit excellent agreement with experiment and show that a comprehensive account of spatial nonuniformity and propagation is necessary to accurately measure the intrinsic damping rate.
A theory is developed for dispersion characteristics of spin waves in ferromagnetic films taking into account both the dipole-dipole and the exchange interactions. An arbitrary orientation of the internal bias magnetic field is assumed. The general case of mixing exchange boundary conditions (surface spin pinning conditions) is considered. The simple analytical dispersion equations are obtained using the classical perturbation theory. The modification of the spin wave spectrum due to surface anisotropy (or pinning conditions) is discussed.