Directional spin hall NANO-antennas

Abstract

Spin-Hall nano-antenna (SHNA) devices are disclosed which leverage the inverse spin Hall effect and spin pumping to receive electromagnetic signals and convert them to electrical signals. Transmitter functionality is also enabled by exemplary SHNA devices. Some disclosed antennas are compatible with acoustic antenna functionalities but may also be configured to not include any acoustic functionalities. Omission of acoustic functionality requirements allows some embodiments to be fabricated on silicon wafers and hence become compatible with mainstream silicon technology. Directionality (radiation or reception patterns) of respective SHNA devices may be determined by use of different anisotropic shapes / geometries. Multiple SHNA can be fabricated on the same chip and made to radiate with different intensities in different directions for multiple-input-multiple-output (MIMO) functionality.

Description

[0001] DIRECTIONAL SPIN HALL NANO- ANTENNAS

[0002] GOVERNMENT SUPPORT CLAUSE

[0003] This invention was made with government support under grant number 2235789 awarded by the National Science Foundation (NSF). The US government has certain rights in the invention.

[0004] CROSS-REFERENCE TO RELATED APPLICATIONS

[0005] This application claims the benefit of U.S. Provisional Patent App. No. 63 / 675,954, filed July 26, 2024, the complete contents of which are herein incorporated by reference.

[0006] FIELD OF THE INVENTION

[0007] Embodiments generally relate to subwavelength antennas and, more particularly, extreme sub wavelength electromagnetic antennas with high radiation efficiency.

[0008] BACKGROUND

[0009] It is well-known in the context of conventional antennas that the gain, bandwidth, and radiation efficiency will plummet if the antenna dimension is shrunk to small fractions of the electromagnetic wavelength that it radiates. This is the case if the antenna is actuated by electromagnetic resonance. There is a school of thought that believes that if an antenna is actuated by acoustic resonance instead of electromagnetic resonance, then the effective wavelength that matters will be the acoustic wavelength at the frequency of radiation and not the electromagnetic wavelength. Since the former is typically five orders of magnitude smaller than the latter, this will allow antennas to be miniaturized to small fractions of the electromagnetic wavelength without sacrificing radiation efficiency or gain. This prompted significant research in acoustically actuated magneto-electric antennas of various types. Some exemplary acoustically actuated antennas by the inventors of the present technology are disclosed in PCT / US2020 / 023941 , filed March 20, 2020, which is incorporated herein in its entirety by reference. Their intrinsic radiation efficiencies did beat the theoretical limit on the radiation efficiencies of conventional antennas actuated by electromagnetic resonance, sometimes even by many orders of magnitude, which lends credence to this idea.

[0010] Actuation of antennas by acoustic radiation has its own limitations, however, and not all applications are suited to accommodating on wafer acoustic waves. Furthermore, acoustic wave generation requires a piezoelectric substrate which is often not compatible with silicon technology, the mainstay of electronics. Therefore, other options for antenna miniaturization are needed.

[0011] SUMMARY

[0012] According to an aspect of exemplary embodiments, spin Hall nano-antenna (SHNA) devices are presented which are not actuated acoustically and are of a completely different flavor from antenna devices which require surface acoustic waves (SAWs) to operate. Exemplary antennas of this disclosure can be implemented on a silicon substrate and are hence fully compatible with mainstream electronics. This new genre of antennas opens a new direction in electrically small antennas whose dimensions are orders of magnitude smaller than the electromagnetic wavelength, and yet they radiate efficiently. According to some exemplary SHNA devices of this disclosure, included nanomagnets which function as antenna elements are sized smaller (e.g., 2-3 orders of magnitude smaller) than the wavelengths of the emitted or incident electromagnetic waves, and receiving gain of the array of nanomagnets is larger (e.g., 2- 3 orders of magnitude larger) than that of a conventional electromagnetic receiving antenna working on the principle of charge fluctuation and / or dipole resonance of the same dimensions.

[0013] Exemplary embodiments configured for receiving electromagnetic waves (receiver antenna) are configured to leverage two distinct processes: (i) the inverse spin Hall effect and (ii) spin pumping. The inverse spin Hall effect is a phenomenon where a spin current in a material is converted into an electrical current. To leverage the inverse spin Hall effect, nanomagnets are configured so that incident EM waves excite confined spin waves in the nanomagnets. The confined spin waves cause spin pumping into heavy metal nanostrips placed in contact with at least part of the nanomagnets. This results in spin currents of alternating spin polarization in the nanomagnets, which induces an alternating charge current / voltage in the nanostrip of heavy metal by virtue of the inverse spin Hall effect. This alternating charge current / voltage matches the frequency of the electromagnetic waves. The current / voltage is output through electrical connections to further circuitry, and the fully electrical signal can then be read by circuitry with ammeter and / or voltmeter functionalities.

[0014] According to some embodiments, an exemplary spin Hall nano-antenna (SHNA) includes an array of ledged magnetostrictive nanomagnets deposited on a substrate, with a heavy metal nanostrip overlying or underlying the ledges. An alternating charge current is passed through the nanostrip and generates an alternating spin-orbit torque in the nanomagnets via the spin Hall effect which makes their magnetizations oscillate in time with the frequency of the current, producing confined spin waves (magnons) within the nanomagnets. The nanomagnets act as cavities for the confined spin waves which radiate electromagnetic waves (photons) in space with the same frequency as the ac current, thereby acting as a “transmitting” nano-antenna. Despite being much smaller than the radiated wavelength, the SHNA surprisingly does not act as a point source which would radiate isotropically. Instead, there is clear directionality (anisotropy) in the radiation pattern, which is also frequency-dependent. This is due to the intrinsic anisotropy in the confined spin wave patterns generated within the nanomagnets.

[0015] According to some embodiments, an exemplary spin Hall nano-antenna (SHNA) includes an array of nanomagnets which are not necessarily ledged and which may or may not be magnetostrictive. A heavy metal nanostrip is positioned on top of or under a portion up to an entirety of a surface of each magnet. One or more nanostrips may be employed to reach all nanomagnets.

[0016] According to some embodiments, a method is disclosed of receiving, detecting, and measuring one or more of intensity, spectra, and polarization of incident electromagnetic waves (a “receiving” nano-antenna), the method comprising: exposing an array of nanomagnets to the electromagnetic waves, wherein the nanomagnets are configured such that the electromagnetic waves cause magnetizations of the nanomagnets to oscillate in time with a frequency of the electromagnetic waves; inducing, with the oscillating magnetizations, an alternating charge current / voltage in a nanostrip of heavy metal positioned on or under at least a portion of the nanomagnets via spin pumping and the inverse spin Hall effect, wherein the alternating charge current / voltage matches the frequency of the electromagnetic waves; and outputting the alternating charge current / voltage, resulting in the transduction of the incident electromagnetic wave to a charge current / voltage to implement a receiving antenna.

[0017] According to some embodiments, directionality (of radiation patterns or reception patterns) of respective SHNA devices may be selected, controlled, or tuned by using different anisotropic shapes / geometries from among a plurality of available anisotropic shapes / geometries. An exemplary SHNA device includes a plurality of nanomagnets which behave together as a “point source” or “point receiver” of EM waves because it is much smaller than the electromagnetic wavelength. However, the “point source” has internal anisotropy since the spin waves generated within the nanomagnets have different amplitudes and phases in different directions. That causes anisotropy in the radiation pattern. This happens because of the anisotropic shape and geometry of the nanomagnets employed. Exemplary embodiments may instead achieve directionality using nanomagnets with isotropic shape and geometry, but the separation between neighboring nanomagnets is different in different directions, which breaks rotational symmetry in space.

[0018] Some embodiments may be configured for compatibility with features and functionalities which require acoustics like surface acoustic waves (SAWs). If desired, embodiments may be configured to function as both electromagnetic antennas and acoustic antennas. Some embodiments provide a dual electromagnetic and acoustic nano-antenna based on the spin Hall effect and / or inverse spin Hall effect. Some embodiments may include a dual electromagnetic / acoustic antenna configured for transmitting, receiving, or both transmitting and receiving. Such a dual antenna may radiate an electromagnetic wave into the surrounding medium or surrounding space (e.g., air or vacuum) and simultaneously radiate an acoustic wave in an underlying substrate. Such a dual antenna may detect and allow for characterization of incident EM waves as well as incident acoustic waves. In either case, an exemplary dual antenna radiates / receives far more efficiently than a conventional antenna of the same size.

[0019] In some embodiments, a particular advantage is SHNA devices configured to be free of acoustic features. Exemplary methods may, for various end applications in which it is desirable, be entirely free of the use of acoustics (such as but not limited to surface acoustic waves) for operations such as but not limited to receiving, detecting, and measuring intensity, spectra, and polarization of incident electromagnetic waves. Exemplary methods may, for various end applications in which it is desirable, be entirely free of the use of acoustics (such as but not limited to surface acoustic waves) for operations such as but not limited to transmitting electromagnetic waves. Exemplary devices and methods may, for various end applications in which it is desirable, be entirely free of the use of acoustics (such as but not limited to surface acoustic waves) for operations such as but not limited to transmitting and receiving electromagnetic waves.

[0020] According to some exemplary embodiments configured for transmission, the wavelength of an emitted EM wave may be determined solely by a frequency (or the frequencies) of the alternating charge current (which is the dominant frequency of the generated EM wave) injected into nanostrips in contact with nanomagnets. According to some exemplary embodiments configured for receiving, the wavelength of a received EM wave may be determined solely by a frequency (or the frequencies) of the alternating charge current (which is the dominant frequency of the received EM wave) detected from the nanostrips which are in contact with nanomagnets receiving the EM wave. Whether transmitting or receiving, exemplary embodiments bear the advantage that the size of the nanomagnets (antenna elements) impose no limit on electromagnetic wavelengths which may be transmitted or received. The antenna elements may be much smaller than the size of the wavelength emitted or detected. The result is a subwavelength antenna with a radiation efficiency that exceeds the theoretical limit for an acoustic antenna excited at acoustic resonance.

[0021] According to some exemplary embodiments, an SHNA device may be free of any piezoelectric elements.

[0022] According to some exemplary embodiments, an SHNA device may be free of any magnetostrictive elements.

[0023] According to some exemplary embodiments, an SHNA device may include magnetostrictive elements but be free of piezoelectric elements.

[0024] Exemplary embodiments may be used in many communication systems such as but not limited to cell phones, radars, etc., and this technology allows all such end use application devices to be aggressively miniaturized because an antenna in accordance with this disclosure can be orders of magnitude smaller than the wavelength. Because it can be very small and yet radiate or receive effectively, an exemplary SHNA device can find use in medically implanted antennas and stealth listening devices for defense and crime-fighting applications, too. Some exemplary embodiments are configured to receive / detect electromagnetic waves. These embodiments may further be configured for measuring intensity, spectra, and / or polarization of the incident electromagnetic waves.

[0025] An exemplary method may comprise the following steps: exposing an array of nanomagnets to the electromagnetic waves, wherein the nanomagnets are configured such that the electromagnetic waves cause magnetizations of the nanomagnets to oscillate in time with a frequency of the electromagnetic waves; inducing, with the oscillating magnetizations, an alternating charge current / voltage in a nanostrip of heavy metal positioned on or under at least a portion of the nanomagnets via spin pumping and the inverse spin Hall effect, wherein the alternating charge current / voltage matches the frequency of the electromagnetic waves; and outputting the alternating charge current / voltage, resulting in the transduction of the incident electromagnetic wave to a charge current / voltage to implement a receiving antenna.

[0026] Some exemplary embodiments comprise a composite antenna. An exemplary composite antenna comprises a single wafer; a plurality of spin Hall nano-antennas (SHNAs) on the single wafer, each SHNA having a different arrangement of nanomagnets, each different arrangement causing the respective SHNA to have a unique radiation pattern among the plurality of SHNAs; and circuitry configured for (i) sending respective alternating charge currents to multiple ones of the plurality of SHNAs, the respective alternating charge currents passing through heavy metal nanostrips in contact with the nanomagnets and generating alternating spin-orbit torques in the nanomagnets via the spin Hall effect which makes magnetizations of the nanomagnets oscillate in time with the frequency of the alternating charge current, producing confined spin waves within the nanomagnets such that the nanomagnets act as cavities for the confined spin waves which radiate electromagnetic waves in space with the same frequency as the respective alternating charge current, such that the composite antenna radiates in different directions with different intensities at the same time, and / or (ii) detecting and measuring one or more of intensity, spectra, and polarization of alternating charge currents which are output by the one or more of the SHNAs in response to exposure to incident electromagnetic waves which the SHNAs convert to charge currents via spin pumping and the inverse spin Hall effect.

[0027] According to some exemplary composite antennas, each SHNA has a different arrangement of nanomagnets by (i) one or more of the SHNAs having nanomagnets of a unique anisotropic geometry from the nanomagnets of other ones of the SHNAs and / or (ii) one or more of the SHNAs having different separations between neighboring nanomagnets that are different in different directions, which breaks rotational symmetry in space.

[0028] According to some exemplary embodiments, a sub wavelength electromagnetic antenna comprises an array of nanomagnets deposited on a substrate; one or more heavy metal nanostrips deposited on the substrate and in contact with the nanomagnets; and circuitry configured to (i) pass an alternating charge current through the one or more heavy metal nanostrips to cause alternating spin-orbit torque in the nanomagnets and / or (ii) receive an alternating charge current from the one or more heavy metal nanostrips. The nanomagnets are configured (i) such that magnetizations of the nanomagnets oscillate when subject to the alternating spin-orbit torque, wherein the oscillating magnetizations cause the array of nanomagnets to radiate an electromagnetic wave, and / or (ii) to cause an alternating charge current in the one or more heavy metal nanostrips via spin pumping and the inverse spin Hall effect when exposed to incident electromagnetic waves. In addition, the subwavelength electromagnetic antenna is characterized by one or more of the following: (i) the nanomagnets are fully clamped on one side by the substrate and on an opposite side by the one or more heavy metal nanostrips, (ii) the one or more heavy metal nanostrips are positioned between the substrate and the nanomagnets, (iii) the nanomagnets are not magnetostrictive or are weakly magnetostrictive, (iv) the nanomagnets comprise iron (Fe), (v) the substrate is not piezoelectric, and (vi) the substrate is a silicon substrate.

[0029] BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic of an exemplary spin Hall nano-antenna (SHNA) device.

[0031] Figure 2 is another schematic of the exemplary SHNA device of Figure 1.

[0032] Figure 3 shows an exemplary magnetostrictive nanomagnet shape involving a main body and a ledge.

[0033] Figures 4A and 4B illustrate the principle of actuating an antenna by spin-orbit torque from a heavy metal nano strip.

[0034] Figure 5 is a scanning electron micrograph of a prototype spin Hall nano-antenna device fabricated in a lab, showing example structural dimensions.

[0035] Figure 6 is a schematic of another exemplary SHNA device. Figure 7 is another schematic of the SHNA device of Figure 6.

[0036] Figure 8 is a schematic of yet another exemplary SHNA device.

[0037] Figure 9 is another schematic of the SHNA device of Figure 8.

[0038] Figure 10 is a diagram of a composite antenna suitable for multiple input multiple output (MIMO) applications.

[0039] Figure 11 is electromagnetic radiation spectrum for real and control samples of prototype SHNAs when the frequency of the ac current pumped into the Pt nanostrip was set to 3 GHz and the input power was 15 dbm. The distance between the receiving horn antenna and the sample in this Example was 81 cm which is 8 times the wavelength, ensuring that the measurements were of the far-field radiation.

[0040] Figure 12 is radiation patterns at different frequencies in the plane of the nanomagnets of the samples tested in the Example. The patterns are shown for both the real sample and the control sample, as well as for both horizontal and vertical polarizations.

[0041] DETAILED DESCRIPTION

[0042] Figures 1 and 2 are schematics of an exemplary spin Hall nano-antenna (SHNA) device 100. The SHNA device 100 comprises an array 101 of nanomagnets 103 of anisotropic geometry on a single substrate 109. A heavy metal (HM) nanostrip 102 (e.g., made of platinum (Pt)) overlies at least part of each of the nanomagnets. A suitable alternative configuration is at least part of each nanomagnet overlies a nanostrip. The illustration of Figure 1 may be understood to represent both of these alternatives.

[0043] The array 101 of nanomagnets comprises one or more (e.g., a plurality) of rows (which may be called columns depending on the reference frame). As illustrated, Figure 1 depicts just three rows, each row comprising one nanostrip 102 and five nanomagnets 103a-e. The second and third illustrated rows are not labeled to avoid overcrowding the figure. In Figure 2, the three rows are only depicted has having three nanomagnets apiece, again for reason of space constraints and not to imply a limit on the number of nanomagnets per row. It will be understood that embodiments may have significantly more than three rows, e.g., hundreds or thousands or millions or more rows. In any case, each row generally comprises a plurality of nanomagnets 103. In practice embodiments may have tens, hundreds, thousands, or more nanomagnets per row. The nanomagnets of any one row are collectively in contact with a shared heavy metal nanostrip 102. Each row has a separate nanostrip 102. All of the nanostrips 102 arc electrically connected with conductive contacts 104 and 105. Radiation from the SHNA device 100 or reception sensitivity of the SHNA device 100 may be increased or decreased by respectively increasing or decreasing the number of nanomagnets in the array 101. The nanomagnets 103 collectively form a single antenna, not an array of separate antennas (e.g., as is the case in a conventional phased array).

[0044] Conductive contacts 104 and 105 are respectively connected with electrodes 106 and 107. The connections of successively larger conductive elements (102 to 104 / 105 to 106 / 107) is not strictly necessary in all embodiments but may be used to facilitate ease of manufacturing for the connection of the antenna array 101 with remaining circuitry 108 which supports the operation of the antenna 101. As a reminder of scale of the illustrated elements, each nanomagnet 103 may be, for example, only 100-500 nm in length and / or 100-500 nm in width. Electrodes 106 and 107 are significantly larger and are provided for connecting to circuitry 108 by conductive traces 110 and 111, respectively. The circuitry 108 may be on the same chip / wafer as the array 101 or, alternatively, may be separate from the chip / wafer of the array 101.

[0045] The SHNA device 100 may be configured to operate at least as a receiving antenna. The nanomagnets 103 are configured such that incident electromagnetic waves 201 cause magnetizations of the nanomagnets 103 to oscillate in time with a frequency of the electromagnetic waves 201. The oscillating magnetizations induce an alternating charge current / voltage in the nanostrip 102 of heavy metal positioned on or under at least a portion of the nanomagnets 103 via spin pumping and the inverse spin Hall effect. The alternating charge current / voltage matches the frequency of the electromagnetic waves 201. The array 101 outputs the alternating charge current / voltage to circuitry 108, resulting in the transduction of the incident electromagnetic wave 201 to a charge current / voltage, thereby implementing a receiving antenna. The circuitry 108 may include such generally well established antenna circuitry such as but not limited to one or more drivers, one or more analog-to-digital (A / D) convertors, one or more signal amplifiers, and / or impedance matching transmission lines or networks.

[0046] The SHNA device 100 may instead or additionally be configured to operate as a transmitting antenna. In such case the circuitry 108 may include a driver for driving the antenna array 101. An alternating current controlled by circuitry 108 is pumped into the nanostrips 102 which injects spin currents of alternating spin polarization into the nanomagnets 103 via the spin Hall effect to cause alternating spin-orbit torque that results in cither back-and-forth domain wall motion in the nanomagnets or magnetization precession, or both, which excites confined spin waves in the nanomagnets 103. The spin waves are time varying magnetizations (mimicking oscillating magnetic dipoles) that can radiate electromagnetic waves into the surrounding medium or surrounding space (e.g., air or vacuum).

[0047] Figure 3 shows a perspective view of a single nanomagnet 103. Each nanomagnet 103 comprises a ledge 431 and a remaining portion 432. The remaining portion 432 may be rectangular, for example, with the ledge 431 being substantially smaller in surface area and volume than the remaining portion 432. Portions 431 and 432 may be a single body produced in a single step or by the same manufacturing steps (e.g., of a photolithographic process). The heavy metal (HM) nanostrip 102 is deposited to overly the ledges 431 of the nanomagnets 103, or else be positioned under the ledges 431. An exemplary nanomagnet 103 may be a magnetostrictive nanomagnet. An exemplary nanomagnet 103 may be a magnetostrictive ferromagnet. An exemplary nanomagnet 103 may be made of Cobalt (Co), for example.

[0048] In Figures 4A and 4B, a single heavy metal strip 102 is arranged across the ledge of each of the nanomagnets 103a, 103b, and 103c. That is to say, each ledge is underneath the heavy metal nanostrip. An exemplary heavy metal is platinum. The bulk of each nanomagnet (the portion 432) is outside the strip 102 and hence its expansion / contraction is not clamped by the nanostrip. Only the ledges are clamped by the nanostrip 102.

[0049] Figures 4A and 4B illustrate the mechanism by which the magnetizations of the nanomagnets are periodically changed, resulting in the emission of one or more waves. In a receiving mode, incident electromagnetic waves cause the magnetizations of the nanomagnets to be periodically changed. Each of Figures 4A and 4B show the same three nanomagnets 103a, 103b, and 103c belonging to the same row of an array such as array 101.

[0050] Figure 4A shows a charge current to the heavy metal nanostrip in a first direction of current, whereas Figure 4B shows a charge current to the heavy metal nanostrip in a second direction of current, where the first and second directions are opposite. Both directions may be result of an applied alternating current for purposes of implementing a transmitting antenna. Thus in practice, the driver of circuitry 108 would periodically alternate the current between these two states. When a charge current is injected into the nanostrip, the top and bottom surfaces of the nanostrip become spin -polarized because of the giant spin Hall effect in the heavy metal (here, Pt). The two surfaces have antiparallcl polarizations. The polarizations of spins in cither surface depends on the direction of the current and changes sign when the current reverses direction. The accumulated spins in the bottom surface of the nanostrip 102 diffuse into the ledges 431 that they are in contact with, and from there into the remaining portion of the nanomagnets 103a, 103b, and 103c. This transfer exerts a spin-orbit torque on the nanomagnets 103a, 103b, and 103c and rotates their magnetizations. Figures 4A and 4B are labeled with a number of arrows to show the spin on top surfaces of the nanostrip 102, the bottom surfaces of the nanostrip 102, and in the nanomagnets 103a, 103b, and 103c.

[0051] When the driver in circuitry 108 reverses the direction of the injected charge current, the change in current reverses the spin polarization of the bottom surface of the nanostrip and hence rotates the magnetizations of the nanomagnets in the opposite direction because the spin-orbit torque will reverse direction. Generally, this will happen only as long as the period of the current is longer than the time of magnetization rotation. Thus, if the driver passes an alternating current through the nanostrip, it will rotate or flip the magnetizations of the nanomagnets periodically, as long as the frequency of the current is considerably smaller than the inverse of the spin rotation times of the nanomagnets. One or more of the shape, size, and material of the nanomagnets, the nanostrip, and the physical arrangement of the nanomagnets and nanostrips may be configured at the time of manufacture to set the threshold to a predetermined value. Figure 5 is a scanning electron micrograph of a prototype spin Hall nano-antenna device fabricated in a lab, showing example structural dimensions.

[0052] The alternating rotation of the nanomagnets in the array 101 causes the array to emit an electromagnetic wave, hence the SHNA device 100 (Figures 1 and 2) will act as an electromagnetic (EM) antenna actuated by electrical signals (as opposed to actuation by an acoustic signal for instance).

[0053] Configurations with nanomagnets 103 that are ledged and the nanostrip 102 placed only over (or under) the ledges 431 (and not over or under the remainders 432 of the nanomagnets 103) is advantageous for some embodiments which include magnetostriction and / or piezoelectric features in their operation. (Such configurations are not necessary in all embodiments, however; some alternatives are discussed below in connection with further figures.) A magnetostrictive nanomagnet (such as but not limited to a cobalt nanomagnet) physically expands and contracts when its magnetization alternates with the frequency of the pumped ac current (in a transmission mode) or with the frequency of incident radiation (in a receiving mode). Were the nanostrip 102 placed directly on the entirety of the nanomagnets to generate the alternating spin-orbit torque, the nanostrip would “clamp” the nanomagnets and prevent the expansion / contraction, which can quench the spin waves and encumber the radiation or receiving process. It is significant to not clamp (or at a minimum to not clamp most of) the body of each of the nanomagnets in embodiments which employ magnetostrictive properties of the nanomagnets. By placing the nanostrip only on the ledges, the expansion / contraction of the bulk of the nanomagnets is not encumbered.

[0054] In the array 101 of Figures 1 and 2, the bottom surfaces of the nanomagnets 103 are clamped by the underlying substrate 109, but this does not hinder the expansion / contraction of the top layers of the nanomagnets 103 and hence does not prevent the generation of confined spin waves within the nanomagnets, which radiate electromagnetic waves, or which are generated by exposure to incident electromagnetic waves.

[0055] In some implementations, the substrate 109 is a piezoelectric substrate. Making the nanomagnets 103 expand and contract with the frequency of the ac current (which requires sufficient magnetostriction, and thus the careful consideration of clamping) generates a timevarying strain in the substrate 109 underneath, thus executing a “breathing mode” oscillation, causing a surface acoustic wave (SAW) of the same frequency as the ac current to propagate in the substrate 109. That SAW may be picked up with transducers (e.g., interdigitated transducers, IDTs, not depicted in the figures) arranged on the same substrate 109. This will make this construct act as a dual electromagnetic and acoustic antenna that, in a transmission mode, radiates an electromagnetic wave into space while simultaneously radiating an acoustic wave in the underlying substrate. A driver in circuitry 108 may be configured to modulate a frequency of the emitted wave solely by controlling a frequency of the alternating charge current. The acoustic antenna functionality was already demonstrated by the inventors of the present technology in PCT / US2020 / 023941, filed March 20, 2020, which is incorporated herein in its entirety by reference.

[0056] Embodiments which have only a portion of each nanomagnet in contact with a nanostrip exhibit a tradeoff of advantages and disadvantages. They are advantageous for applications in which magnetostrictive effects are needed, e.g., when it is desired for an antenna with dual electromagnetic and acoustic properties. An intertwined disadvantage, however, is that such configuration may risk precluding sufficient spin pumping because only a relatively small section of the nanomagnets may be in contact with the nanostrip. Acoustic free embodiments may advantageously avoid this tradeoff entirely.

[0057] Figures 6 and 7 depict an SHNA device 600 which does not require any acoustic functionalities. The SHNA device 600 includes an array 601 of nanomagnets 603 (including nanomagnets 603a-e in the first row) and nanostrips 602 where at least a majority and up to an entirety (the latter scenario being depicted) of the nanomagnets 602 are under nanostrips 602. The nanomagnets 603 may be mostly or entirely clamped (on one side) by the nanostrips 602. The clamping is not a problem, however, as the nanomagnets 603 of SHNA device 600 are made of non-magnetostrictive or weakly magnetostrictive ferromagnet material like Fe (instead of Co) and do not experience appreciable expansion / contraction when their magnetization alternate with the frequency of the pumped ac current (in a transmission mode) or with the frequency of incident radiation (in a receiving mode). The large amount of overlap (e.g., total overlap) of nanomagnets and nanostrip maximizes the spin pumping. The substrate can be either piezoelectric (e.g., if desired for other circuitry which is manufactured on the same wafer) or non-piezoelectric. In any event there is no need for SAWs in connection with the operation of the array 601 as a transmitting antenna or as a receiving antenna. As in other embodiments of this disclosure, the figures are not intended to suggest a limit on the number of nanomagnets per row or per SHNA device. The depiction of only a few rows and a few nanomagnets per row are simply to illustrate a general arrangement which is scalable to include as many rows and nanomagnets per row as desired for a particular application of the technology. The circuitry 108 may be on the same chip / wafer as the array 601 or, alternatively, may be separate from the chip / wafer of the array 601.

[0058] Figures 8 and 9 depict an exemplary SHNA device 800 which does not require any acoustic functionalities but which is suited to operate using nanomagnets which are magnetostrictive or nanomagnets which are nonmagnetostrictive or only faintly magnetostrictive. The SHNA device 800 includes an array 801 of nanomagnets 803 (including nanomagnets 803a- e in the first row) and nanostrips 802 where at least a majority and up to an entirety (the latter scenario being depicted) of the nanomagnets 602 (on one side) are in contact with nanostrips 802. The nanomagnets 803 may be mostly or entirely clamped by the nanostrips 802 on the side of the nanomagnets 803 facing the nanostrips 802. In the depicted orientation, it is the entire bottom sides of the nanomagnets 803 which arc in contact with and clamped by the nanostrips 802. The clamping is not a problem, however, as the nanomagnets 803 of SHNA device 800 are not clamped by any materials or substrates on their sides facing away from the nanostrips 802. In the depicted orientation, the topsides of the nanomagnets 803 are mostly, and in this exemplary case, entirely unclamped. There is little and preferably no material in contact with the topsides of the nanomagnets 803 which is capable of clamping the topsides. In this configuration, the nanomagnets 803 may be made of a magnetostrictive material like cobalt (Co). The bottom surfaces of the nanomagnets 803 are clamped by the underlying nanostrips 802, but this does not hinder the expansion / contraction of the top layers of the nanomagnets 803 and hence does not prevent the generation of confined spin waves within the nanomagnets 803, which radiate electromagnetic waves, or which are generated by exposure to incident electromagnetic waves. As in other embodiments of this disclosure, the figures are not intended to suggest a limit on the number of nanomagnets per row or per SHNA device. The depiction of only a few rows and a few nanomagnets per row are simply to illustrate a general arrangement which is scalable to include as many rows and nanomagnets per row as desired for a particular application of the technology. The circuitry 108 may be on the same chip / wafer as the array 801 or, alternatively, may be separate from the chip / wafer of the array 801.

[0059] In an alternative implementation, the nanomagnets 803 may be made of nonmagneto strictive or weakly magnetostrictive ferromagnet material like Fe (instead of Co) and do not experience appreciable expansion / contraction when their magnetizations alternate with the frequency of the pumped ac current (in a transmission mode) or with the frequency of incident radiation (in a receiving mode). That is to say, the configuration of nanostrips and nanomagnets exemplified by SHNA device 800 is well suited to nanomagnets of all degrees of magnetostriction (from magnets with no magnetostrictive properties to magnets with high magnetostrictive properties). In any case, the large amount of overlap (e.g., total overlap) of nanomagnets and nanostrips maximizes the spin pumping. The substrate 809 can be either nonpiezoelectric or piezoelectric (e.g., if desired for other circuitry which is manufactured on the same wafer). In any event there is no need for SAWs in connection with the operation of the array 801 as a transmitting antenna or as a receiving antenna. Figure 10 is a diagram of an exemplary composite antenna 1000. On the same wafer 1009 multiple spin Hall antennas 1099 arc arranged, each with different arrangements of nanomagnets, each radiating (and / or receiving) primarily in a different direction than the others. The composite antenna 1000 is configured to radiate in (or receive from) different directions at the same time. This may have an application in 6G systems that require MIMO (multiple input and multiple output) antennas, for example. The multiple output requirement is fulfilled by the composite antenna 1000.

[0060] The composite antenna 1000 includes means (in this case circuitry 1008) for sending respective alternating charge currents to multiple ones of the plurality of SHNAs, the respective alternating charge currents passing through heavy metal nanostrips in contact with the nanomagnets and generating alternating spin-orbit torques in the nanomagnets via the spin Hall effect which makes magnetizations of the nanomagnets oscillate in time with the frequency of the alternating charge current, producing confined spin waves within the nanomagnets such that the nanomagnets act as cavities for the confined spin waves which radiate electromagnetic waves in space with the same frequency as the respective alternating charge current, such that the composite antenna radiates in different directions at the same time. Note that wired connection between the control circuitry 1008 and the individual antennas 1099 is not depicted in Figure 10.

[0061] Figure 10 shows how different shapes or different dimensions of like shapes can be used to achieve SHNA devices 1099 which have different radiation patterns (including different radiation directions) to one another. Likewise, different shapes or different dimensions of like shapes can be used to achieve SHNA devices which have different directional sensitivity. It should be noted that whatever the impression conveyed by the literal image of Figure 10, each of the SHNA devices 1099 may be configured in accordance with any embodiment of this disclosure. Accordingly, each antenna may be exclusively an electromagnetic antenna (with no acoustic functionality), an acoustic antenna, or a dual EM / acoustic antenna. In each device 1099 the nanomagnets may be over or else under nanostrips. In each device 1099 the extent of contact between the nanomagnets and the nanostrips may be a minority of a side of each nanomagnet, a majority of a side of each nanomagnet, or an entirety of a side of each nanomagnet. EXAMPLE. Electromagnetic Radiation Spectrum

[0062] Two sets of samples were fabricated nominally identical and in accordance with Figure 1, except one sample included nanomagnets and the other did not. The latter is called the “control sample” in this Example and served to help separate out extraneous contributions to the electromagnetic spectrum. The spectrum of the radiation the control sample emitted was measured for comparison with that of the “real sample” which contained the nanomagnets.

[0063] The spectra of the electromagnetic radiation emitted by the samples was measured in an anechoic chamber, with the detecting horn antenna facing the plane of the nanomagnets as shown in the inset of Figure 11. The radiation measured by the horn antenna in the anechoic chamber was not solely due to the nanomagnets, but also has contributions from the Pt nanostrip, the contact lines, the contact pads and any other extraneous source of radiation. The control sample assisted in differentiating these sources of EM radiation from the EM radiation emitted by the nanomagnet array of the real sample.

[0064] A spectrum analyzer was connected to the horn antenna to measure the spectrum of the received emission. The sample was placed at a distance of 81 cm from the horn antenna to ensure that we are always measuring the far-field radiation at the excitation frequency. The input power from the ac current source was set to 15 dbm (31 mW). Figure 11 shows the measured spectra from both the real sample and the control sample.

[0065] The observed difference between the powers received from the real and the control sample is small in magnitude. The power received from the real sample by the horn antenna of receiving area 3 cm x 3 cm was -55 dbm (3.16 nW) whereas that received from the control sample was -57.5 dbm (1.77 nW). The difference of 1.4 nW, albeit well above the noise floor in the anechoic chamber [which was -120 dbm (1 pW)], was too small to allow for making any quantitative estimates, given the limited sensitivities of the measuring equipment. Furthermore, as discussed below, the nanomagnets radiate anisotropically, so that the difference between the power received from the real sample and the control sample will be different in different directions for the same source-detector separation.

[0066] Figure 11 shows satellite peaks in the radiation spectrum that are present in both the real sample and the control sample. They are much weaker than the main peak. These satellite peaks are either from extraneous sources, or generated by the peripherals. The spectrum was also measured of the scattering parameter S1 1 with a vector network analyzer, and that data arc shown in Figure 12. There arc two sharp notches in the Si l spectrum at 3.1 and 5.8 GHz, showing stronger coupling from the alternating current source into the sample at these frequencies. Because of this, the spectrum of the emitted radiation was measured with the driving alternating current frequency set to 3 GHz.

[0067] The radiation patterns of the SHNA were also measured in three different planes - the plane of the nanomagnets and the two transverse planes. They were measured at frequencies of 1, 2, 3, 4, 5 and 6 GHz (wavelengths 5 - 30 cm). The detector was always placed at a distance of 81 cm from the sample, which means that the far-field radiation pattern was detected. The patterns were measured for both the real sample and the control sample. The results are shown in Figure 12 for both horizontal and vertical polarizations in the plane of the nanomagnets. Since the radiation pattern of the real sample is very significantly different from that of the control sample, it can be concluded that the nanomagnets are radiating. This is further confirmatory evidence of the spin Hall nano-antenna (SHNA) operation.

[0068] In Figure 12, the difference between the radiation from the real sample and the radiation from the control sample varies quite strongly with direction, which means that the nanomagnets are radiating anisotropically. This anisotropy is surprising since the lateral dimension of the entire nanomagnet array (~ 160 pm) is much smaller than the electromagnetic wavelength at all measurement frequencies. Hence the entire nanomagnet array could be viewed as a point source that should radiate isotropically. Yet, it does not. This happens because the “point source” has internal anisotropy since the spin waves generated within the nanomagnets have different amplitudes in different directions. That causes the anisotropy in the radiation pattern. This happens because of the anisotropic shape and geometry of the nanomagnets employed.

[0069] It is noted that, as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely”, “only”, and the like in connection with the recitation of claim elements, or use of a “negative” limitation.

[0070] As will be apparent to those of skill in the ail upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. Any recited method can be carried out in the order of events recited or in any other order which is logically possible.

[0071] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.

[0072] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, representative illustrative methods and materials are described.

[0073] It is to be understood that the terminology and explanations used herein are for the purpose of describing exemplary embodiments only, and are not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A composite antenna, comprising a single wafer; a plurality of spin Hall nano-antennas (SHNAs) on the single wafer, each SHNA having a different arrangement of nanomagnets, each different arrangement causing the respective SHNA to have a unique radiation pattern among the plurality of SHNAs; and circuitry configured for(i) sending respective alternating charge currents to multiple ones of the plurality of SHNAs, the respective alternating charge currents passing through heavy metal nanostrips in contact with the nanomagnets and generating alternating spin-orbit torques in the nanomagnets via the spin Hall effect which makes magnetizations of the nanomagnets oscillate in time with the frequency of the alternating charge current, producing confined spin waves within the nanomagnets such that the nanomagnets act as cavities for the confined spin waves which radiate electromagnetic waves in space with the same frequency as the respective alternating charge current, such that the composite antenna radiates in different directions with different intensities at the same time, and / or(ii) detecting and measuring one or more of intensity, spectra, and polarization of alternating charge currents which are output by the one or more of the SHNAs in response to exposure to incident electromagnetic waves which the SHNAs convert to charge currents via spin pumping and the inverse spin Hall effect.

2. The composite antenna of claim 1, wherein each SHNA has a different arrangement of nanomagnets by (i) one or more of the SHNAs having nanomagnets of a unique anisotropic geometry from the nanomagnets of other ones of the SHNAs and / or (ii) one or more of the SHNAs having different separations between neighboring nanomagnets that are different in different directions, which breaks rotational symmetry in space.

3. The composite antenna of claim 1 , wherein the plurality of SHNAs are deposited on a piezoelectric substrate of the single wafer.

4. The composite antenna of claim 1, wherein the plurality of SHNAs are deposited on or over a nonpiezoelectric substrate of the single wafer.

5. The composite antenna of claim 1, wherein the plurality of SHNAs are deposited on a silicon substrate of the single wafer.

6. The composite antenna of claim 1, wherein the nanomagnets of the plurality of SHNAs are magnetostrictive.

7. The composite antenna of claim 1, wherein the nanomagnets of the plurality of SHNAs are non-magnetostrictive or weakly magnetostrictive.

8. A sub wavelength electromagnetic antenna, comprising an array of nanomagnets deposited on a substrate; one or more heavy metal nanostrips deposited on the substrate and in contact with the nanomagnets; and circuitry configured to (i) pass an alternating charge current through the one or more heavy metal nanostrips to cause alternating spin-orbit torque in the nanomagnets and / or (ii) receive an alternating charge current from the one or more heavy metal nanostrips, wherein the nanomagnets are configured (i) such that magnetizations of the nanomagnets oscillate when subject to the alternating spin-orbit torque, wherein the oscillating magnetizations cause the array of nanomagnets to radiate an electromagnetic wave, and / or (ii) to cause an alternating charge current in the one or more heavy metal nanostrips via spin pumping and the inverse spin Hall effect when exposed to incident electromagnetic waves, and wherein the subwavelength electromagnetic antenna is characterized by one or more of the following:(i) the nanomagnets arc fully clamped on one side by the substrate and on an opposite side by the one or more heavy metal nanostrips,(ii) the one or more heavy metal nanostrips are positioned between the substrate and the nanomagnets,(iii) the nanomagnets are not magnetostrictive or are weakly magnetostrictive,(iv) the nanomagnets comprise iron (Fe),(v) the substrate is not piezoelectric, and(vi) the substrate is a silicon substrate.

9. The subwavelength electromagnetic antenna of claim 8, wherein the nanomagnets are fully clamped on one side by the substrate and on an opposite side by the one or more heavy metal nano strips.

10. The subwavelength electromagnetic antenna of claim 8, wherein the one or more heavy metal nanostrips are positioned between the substrate and the nanomagnets.

11. The sub wavelength electromagnetic antenna of claim 8, wherein the nanomagnets are not magnetostrictive or are weakly magnetostrictive.

12. The sub wavelength electromagnetic antenna of claim 8, wherein the nanomagnets comprise iron (Fe).

13. The subwavelength electromagnetic antenna of claim 8, wherein the substrate is not piezoelectric.

14. The subwavelength electromagnetic antenna of claim 8, wherein the substrate is a silicon substrate.

15. A non-acoustic method of receiving, detecting and measuring intensity, spectra, and polarization of incident electromagnetic waves, comprising exposing an array of nanomagnets to the electromagnetic waves, wherein the nanomagnets are configured such that the electromagnetic waves cause magnetizations of the nanomagnets to oscillate in time with a frequency of the electromagnetic waves;inducing, with the oscillating magnetizations, an alternating charge current / voltage in a nanostrip of heavy metal positioned on or under at least a portion of the nanomagnets via spin pumping and the inverse spin Hall effect, wherein the alternating charge current / voltage matches the frequency of the electromagnetic waves; and outputting the alternating charge current / voltage, resulting in the transduction of the incident electromagnetic wave to a charge current / voltage to implement a receiving antenna.

16. The method of claim 15, wherein the nanomagnets are sized smaller than the wavelengths of the incident electromagnetic waves, and receiving gain of the array of nanomagnets is larger than that of a conventional electromagnetic receiving antenna working on the principle of charge fluctuation and / or dipole resonance of the same dimensions.

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