Spin-wave switches and filters based on magnetic crystals

Abstract

This invention relates to spin-wave switches and filters based on magnetic crystals. According to one embodiment, a magnetic crystal device may include a ferromagnetic layer and an antiferromagnetic planar periodic structure disposed on the ferromagnetic layer. The magnetic crystal device of this invention can be used as a spin-wave switch to effectively control the transmission coefficient of spin waves, or as a spin-wave filter to filter spin waves of specific frequencies.

Description

Technical Field

[0001] This invention relates generally to the fields of magnetonics and magneton devices, and more particularly to a magneton crystal device and a spin wave switch and filter including the magneton crystal device. Background Technology

[0002] Spin waves, as intrinsic excitations of electron spintron systems in magnetically ordered media, were first proposed by Bloch in 1930. Later, Holstein, Primakoff, and Dyson introduced the concept of the smallest quantized unit of spin waves—the magneton (or simply magneton). Each magneton carries a... Magnetons possess spin angular momentum, thus enabling the transmission of spin information and making them a promising information carrier. Magnetism is the field that studies the use of magnetons for information transmission, storage, and processing. Within magnetism, the manipulation of magneton transport is a crucial branch. Constructing artificial magneton crystals is one of the most effective and commonly used methods for controlling magneton transport.

[0003] As early as 1976, Sykes, Adam, and Collins experimentally studied the propagation characteristics of spin waves (magnetons) in a periodic structure. This work is considered the first study on magneton crystals, although the concept of magneton crystals did not exist at that time. In 2001, Nikitov first proposed the concept of magneton crystals. A magneton crystal is an artificially constructed medium with periodically changing magnetic properties, whose magneton spectrum exhibits significantly different characteristics compared to a homogeneous medium. The magneton spectrum of a magneton crystal has a band structure with band gaps, which prevent spin waves (magnetons) of certain frequencies from passing through. All magneton crystals utilize this frequency selectivity to achieve artificial control over the propagation of spin waves (magnetons).

[0004] Based on the type of interaction considered, spin waves can be mainly divided into two types: (1) spin waves dominated by dipole interaction (magnetostatic spin waves); (2) dipole-exchange spin waves where dipole and exchange interactions coexist; and (3) spin waves dominated by exchange interaction (exchange spin waves). Among them, magnetostatic spin waves are waves with relatively long wavelengths, generally between 0.5 GHz and 10 GHz; exchange spin waves are waves with short wavelengths (generally less than 100 nm) and higher frequencies, generally between 20 GHz and 1 THz; dipole-exchange spin waves are between the two. Magnetonic crystal devices based on magnetostatic spin waves have the advantages of low device fabrication difficulty and easy realization of spin wave excitation and detection; while magnetic crystal devices based on exchange spin waves have the advantages of small device size and fast information processing speed.

[0005] Magnetonic crystals based on magnetostatic spin waves are easier to implement experimentally. Therefore, most traditional magnetonic crystal devices are based on magnetostatic spin waves and do not cover exchanged spin waves and dipole-exchanged spin waves. This will limit the improvement of future magnetonic device performance to some extent.

[0006] In addition to the drawbacks mentioned above, traditional magnetic crystals also suffer from limited device functionality and difficulty in electrical manipulation. Clearly, traditional magnetic crystals still have many limitations for device applications. Therefore, it is necessary to continue exploring new magnetic crystals to overcome the aforementioned or other shortcomings of existing technologies. Summary of the Invention

[0007] One aspect of the present invention provides a magnetic crystal device, comprising: a ferromagnetic layer; and an antiferromagnetic planar periodic structure disposed on the ferromagnetic layer.

[0008] In some embodiments, the antiferromagnetic planar periodic structure includes: a plurality of antiferromagnetic strip structures extending along a first direction and periodically arranged along a second direction perpendicular to the first direction; or a plurality of antiferromagnetic dot structures arranged in a two-dimensional array.

[0009] In some embodiments, the antiferromagnetic strip structure has a rectangular, square, triangular, trapezoidal, or semi-circular cross-sectional shape, and the antiferromagnetic dot structure has a circular, annular, polygonal, or hollow polygonal shape.

[0010] In some embodiments, the number of periods N of the antiferromagnetic planar periodic structure is 5 or more, the width of each structural unit in the antiferromagnetic planar periodic structure is between 100 μm and 3 nm, and the spacing between two adjacent structural units is also between 100 μm and 3 nm. Accordingly, the operating frequency of the magnetic crystal device can be between 0.5 GHz and 1 THz.

[0011] In some embodiments, the ferromagnetic layer has a thickness of 0.5 nm to 15 nm, and the antiferromagnetic planar periodic structure has a thickness of 1 nm to 15 nm.

[0012] In some embodiments, the magnetic crystal device further includes: a spin Hall effect layer disposed on the side of the ferromagnetic layer opposite to the antiferromagnetic planar periodic structure and in contact with the ferromagnetic layer, the spin Hall effect layer being used to flip the magnetic moment of the ferromagnetic layer.

[0013] One aspect of the present invention provides a spin wave switch comprising any one of the above-described magnetic crystal devices.

[0014] In some embodiments, the frequency of the spin wave that is turned on or off by the spin wave switch is in the range of 0.5 GHz to 1 THz.

[0015] One aspect of the present invention provides a spin wave filter comprising any one of the above-described magnetic crystal devices.

[0016] In some embodiments, the frequency of the spin wave filtered by the spin wave filter is in the range of 0.5 GHz to 1 THz.

[0017] The above and other features and advantages of the present invention will become apparent from the following description of exemplary embodiments taken in conjunction with the accompanying drawings. Attached Figure Description

[0018] Figure 1A This is a schematic diagram of the layer structure of a magnetic crystal device according to an exemplary embodiment of the present invention, wherein the magnetic moment of the ferromagnetic layer is in the x-direction.

[0019] Figure 1B This is a schematic diagram of the layer structure of a magnetic crystal device according to an exemplary embodiment of the present invention, wherein the magnetic moment of the ferromagnetic layer is in the y direction.

[0020] Figure 1C This is a schematic diagram of the layer structure of a magnetic crystal device according to an exemplary embodiment of the present invention, wherein the magnetic moment of the ferromagnetic layer is in the z-direction.

[0021] Figure 2 This is the transmission spectrum of a spin wave (magneton) switch according to an exemplary embodiment of the present invention.

[0022] Figure 3 This describes the filtering characteristics of a spin wave (magneton) filter according to an exemplary embodiment of the present invention. Detailed Implementation

[0023] Traditional magneton crystal devices can only control the transmission of magnetostatic spin waves, with operating frequencies mostly between 0.5 GHz and 10 GHz. Furthermore, their functions are limited and they are difficult to control electrically. This inventor proposes a novel magneton crystal device that can be used to control magnetostatic spin waves, as well as exchanged spin waves and dipole-exchanged spin waves. Its operating frequency can vary between 0.5 GHz and 1 THz; its size can be on the order of hundreds of nanometers or smaller, or even on the order of micrometers and millimeters; and it can be controlled by electric current. This magneton crystal device has two main functions: first, as a spin wave (magneton) switch, it can efficiently control the transmission coefficient of spin waves; second, as a spin wave (magneton) filter, it can filter spin waves (magnetons) of specific frequencies. Both of these devices are important building blocks for constructing high-frequency nanomagneton devices.

[0024] It should be noted that the magnetic moment of the ferromagnetic layer in the magnetic crystal device proposed by the inventors can have three directions: x, y, and z, corresponding to three configurations: (1) Type x; (2) Type y; and (3) Type z. These three configurations are respectively as follows: Figure 1A , Figure 1B and Figure 1C As shown, Type x and Type y correspond to the in-plane magnetic moment, while Type z corresponds to the out-of-plane magnetic moment, also known as the perpendicular magnetic moment. Under these three configurations, the spin wave transmission spectrum is exactly the same, meaning the device function is identical. Therefore, in practical applications, the appropriate configuration can be selected based on specific needs.

[0025] Figure 1A This is a schematic diagram of the layer structure of a magnetic crystal device 100 according to an exemplary embodiment of the present invention, a configuration referred to as Type x. For example... Figure 1A As shown, the magnetic crystal device 100 includes a ferromagnetic layer 110 and an antiferromagnetic planar periodic structure 120 formed on the ferromagnetic layer 110. The antiferromagnetic planar periodic structure 120 may include a one-dimensional or two-dimensionally arranged periodic structure. For example, in some embodiments, the antiferromagnetic planar periodic structure 120 may include a plurality of antiferromagnetic strip structures extending along a first direction and periodically arranged along a second direction perpendicular to the first direction, such as... Figure 1A As shown, the first direction is the y-axis direction, and the second direction is the x-axis direction. Alternatively, the antiferromagnetic planar periodic structure 120 may include a plurality of antiferromagnetic point structures arranged in a two-dimensional array along the first and second directions. For example, the antiferromagnetic strip structure discussed herein may have a rectangular, square, triangular, trapezoidal, or semi-circular cross-sectional shape, and the antiferromagnetic point structure discussed herein may have a circular, annular, polygonal, or hollow polygonal shape. It should be understood that the principles of the present invention are not limited to specific antiferromagnetic structure shapes. Figure 1A In the configuration shown, the exchange bias field H of the antiferromagnetic planar periodic structure 120 eb Always along the +x direction, the magnetic moment M of the ferromagnetic layer 110 can be along the +x or -x direction, corresponding to two states: State 1 and State 2 respectively.

[0026] State 1 and State 2 can be driven and switched using a pulsed current method via the spin-orbit torque (SOT) effect. For example, a spin Hall effect layer, typically a heavy metal layer such as a Pt or Ta layer, can be formed on the side of the ferromagnetic layer 110 opposite to the antiferromagnetic planar periodic structure 120. When a current is passed through the heavy metal layer in one direction, due to the spin Hall effect, the charge flow generates a spin current, applying an SOT effect to the magnetic moment M of the ferromagnetic layer 110. Under certain conditions, such as when the current density is sufficiently high, the magnetic moment M of the ferromagnetic layer 110 can be flipped, for example, from +x to -x, that is, the magnetic crystal device 100 changes from State 1 to State 2. Then, when a current is passed through the heavy metal layer in the opposite direction, the magnetic moment M can be restored from -x to +x, that is, the magnetic crystal device 100 returns to State 1 from State 2. Therefore, by controlling the direction of the current, the switching between State 1 and State 2 can be achieved. It should be understood that an auxiliary magnetic field H in the +z direction can be applied during SOT flipping. z Auxiliary magnetic field H z The switching can be achieved through an external magnetic field, interlayer coupling fields, dipole fields, bias fields, or even an equivalent magnetic field generated by an electric field. Therefore, this dual-state switching can be entirely electrically controlled. The mechanism of SOT magnetic reversal is well-known in the art and will not be described in detail here. Since the transmission spectra of State 1 and State 2 are different, for certain specific frequencies of spin waves (magnetons), there exists a situation where one state can almost completely pass through the magneton crystal, while the other state is almost totally reflected and cannot pass through. Therefore, by using SOT to switch between State 1 and State 2, the "on" and "off" states of certain specific frequencies of spin waves (magnetons) can be achieved, constructing a novel spin wave (magneton) switching device. On the other hand, the magneton crystal device 100 in a specific state, such as State 1 or State 2, can be used as a spin wave filter, for example, filtering out spin waves of a specific frequency while allowing spin waves of other frequencies to pass through, i.e., a band-stop filter. When switching between State 1 and State 2, the filtering band of the magnetic crystal device 100 changes. It can be understood that when used as a spin-wave switch or filter, the filtering band of the magnetic crystal device 100 changes on one side (e.g., at...). Figure 1A Spin waves are injected on the left or right side of the device, and on the opposite side (e.g., at the center). Figure 1A Spin waves are detected on the right or left side of the device.

[0027] Figure 1BThis is a schematic diagram of the layer structure of a magnetic sub-crystal device 100 according to an exemplary embodiment of the present invention, a configuration referred to as Type y. Similar to Type x, the magnetic sub-crystal device 100 includes a ferromagnetic layer 110 and an antiferromagnetic planar periodic structure 120. Figure 1A The difference lies in the fact that, under this configuration, the exchange bias field H of the antiferromagnetic planar periodic structure 120 is... eb Always along the -y direction, the magnetic moment M of the ferromagnetic layer 110 can be along either -y or +y, corresponding to two states: State 1 and State 2, respectively.

[0028] Similarly, State 1 and State 2 of the Type y configuration can also be switched using a State of Tilting (SOT). A heavy metal layer can be grown at the bottom of the ferromagnetic layer 110, and currents in different directions can be passed through the heavy metal layer. The SOT generated by the current can change the magnetic moment M from -y to +y, or vice versa, that is, the magnetic crystal device 100 switches between State 1 and State 2. Therefore, like Type x, the magnetic crystal device 100 in the Type y configuration can also be used to construct a novel spin wave (magnetic) switching device or filter device.

[0029] Figure 1C This is a schematic diagram of the layer structure of a magnetic crystal device 100 according to an exemplary embodiment of the present invention, a configuration referred to as Type z. Similar to the previous two configurations, the magnetic crystal device 100 includes a ferromagnetic layer 110 and an antiferromagnetic planar periodic structure 120. The difference is that, in this configuration, the exchange bias field H of the antiferromagnetic periodic structure 120... eb Always along the +z direction. The magnetic moment M of the ferromagnetic layer 120 can be along +z or -z, corresponding to two states: State 1 and State 2, respectively.

[0030] Similarly, the State 1 and State 2 of the Type z configuration can also be switched using a heavy metal layer. A heavy metal layer can be grown at the bottom of the ferromagnetic layer 110, and currents in different directions can be passed through the heavy metal layer. The SOT generated by the current can change the magnetic moment M from +z to -z, or vice versa, that is, the magnetic crystal device 100 switches between State 1 and State 2. Therefore, like the previous two configurations, the magnetic crystal device 100 in the Type z configuration is also a novel spin wave (magnetic) switching device or filter device.

[0031] Understandably, for the Type z configuration, similar to Type x, an auxiliary magnetic field, namely a magnetic field H in the +x direction, can also be used to achieve SOT magnetic reversal. x Auxiliary magnetic field H xThis can be achieved through interlayer coupling fields, dipole fields, or bias fields. Therefore, the two-state switching of the Type z configuration is still entirely electrically controlled and does not require an external magnetic field.

[0032] The antiferromagnetic planar periodic structure 120 described above, as mentioned earlier, includes, but is not limited to, one-dimensional or two-dimensional periodic arrangements. For example, in some embodiments, the antiferromagnetic planar periodic structure 120 may include a plurality of antiferromagnetic strip structures extending along a first direction and periodically arranged along a second direction perpendicular to the first direction, such as... Figure 1A , 1B As shown in 1C, the first direction is the y-axis direction, and the second direction is the x-axis direction. Alternatively, the antiferromagnetic planar periodic structure 120 may include a plurality of antiferromagnetic point structures arranged in a two-dimensional array along the first and second directions. For example, the antiferromagnetic strip structure discussed herein may have a rectangular, square, triangular, trapezoidal, or semi-circular cross-sectional shape, and the antiferromagnetic point structure discussed herein may have a circular, annular, polygonal, or hollow polygonal shape. It should be understood that the principles of the present invention are not limited to specific antiferromagnetic structure shapes.

[0033] For the antiferromagnetic planar periodic structure 120, the period number N is generally 5 or more, and more preferably 10 or more. Calculations show that when the period number N is 5 or more, the two states of the magnetic crystal device 100, namely State 1 and State 2, exhibit different transmittances for spin waves of a specific frequency, and this transmittance difference becomes more significant as the period number N increases. When the period number N reaches 10 or more, the transmittance difference can reach more than 90%, for example, the transmittance corresponding to State 1 is less than 10%, and the transmittance corresponding to State 2 is approximately 100%. Although a large period number N can be used, from the perspective of ease of manufacturing, the period number N can be less than 1000, preferably less than 100.

[0034] In the antiferromagnetic planar periodic structure, the width or diameter of each structural unit is between 100 μm and 3 nm, and the spacing between adjacent structural units is also between 100 μm and 3 nm. Correspondingly, the operating frequency of the magnetic crystal device can be between 0.5 GHz and 1 THz. Calculations show that the size (width or diameter) of the structural unit and the spacing between structural units affect the transmission spectrum of spin waves by the magnetic crystal device 100. Specifically, when the size (width or diameter) of the structural unit and the spacing between structural units change, the spin wave frequency band blocked by the magnetic crystal device 100 also changes accordingly. Therefore, the size and spacing of the structural units can be selected according to the desired spin wave frequency band to be blocked.

[0035] The ferromagnetic layer 110 typically has a thickness of 0.5 nm to 15 nm. From the perspectives of facilitating the flipping of the magnetic moment, maintaining the transmission of the spin wave, and ease of manufacturing, a thickness of 0.5 nm to 3 nm is more preferable. The antiferromagnetic planar periodic structure 120 typically has a thickness of 1 nm to 15 nm. It should be understood that the appropriate thickness can be selected based on the materials of the ferromagnetic layer 110 and the antiferromagnetic planar periodic structure 120.

[0036] For the selection of materials, the ferromagnetic layer 110 includes, but is not limited to: Fe, Co, Ni, Mn, rare earth elements and their metal alloys, such as CoFeB, NiFe, SmCo5, Sm2Co. 17 Nd2Fe 14 Ferromagnetic thin films of type B; Heusler alloys; magnetic metal oxides Fe3O4; garnet R3Fe5O 12 R is one of the following ferromagnetic two-dimensional materials or a combination of several ferromagnetic two-dimensional materials: Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu; and Co2S2, CoBr2, CoC2, Cr2C, CrBr3, CrC2, CrGaTe3, CrI3, CrOBr, CrWGe2Te6, CrWI6, ErSe, EuOBr, FeBr2, FeC2, Fe3GeTe2, FeI2, MnC2, NiBr2, NiC2, NiI2, and VC2.

[0037] The materials of the antiferromagnetic planar periodic structure 120 include, but are not limited to: antiferromagnetic thin films of MnN, IrMn, PtMn, FeMn, and PdMn; and one or a combination of several antiferromagnetic two-dimensional materials of CrPS4, CoI2, CoO2, NiO2, CrI2, CrSe2, FeSe, MnBr2, MnCl2, MnI2, VBr2, and VI2.

[0038] The magnetic crystal device in this invention patent has a certain spin wave (magneton) operating frequency range. The frequency range of the spin wave (magneton) is related to the magnetic moment orientation, the materials of the ferromagnetic layer and the antiferromagnetic planar periodic structure, as well as the size and periodicity of the antiferromagnetic planar periodic structure, as described above, and is generally in the range of 0.5 GHz to 1 THz.

[0039] It is understandable that spin waves can propagate along the periodic alignment direction of an antiferromagnetic planar periodic structure. For example, in Figure 1A , 1BIn 1C, the excitation of spin waves can occur on the left side of the antiferromagnetic planar periodic structure, while reception and detection can occur on the right side, or vice versa. Spin wave excitation methods include, but are not limited to: (1) GSG electrodes; (2) lasers; (3) spin injection. Spin wave detection methods include, but are not limited to: (1) GSG electrodes; (2) lasers; (3) the inverse spin Hall effect. It should be understood that the excitation and detection of spin waves are techniques known in the art and will not be described again.

[0040] Figure 2 This is an example of the transmission spectrum of an exemplary spin wave (magneton) switch according to the present invention, specifically the relationship between the transmission coefficient T and the spin wave (magneton) frequency f. It can be seen that when the spin wave (magneton) frequency f is in the range of 24.5 GHz to 25.5 GHz, the transmission coefficient T1 of State 1 is close to 0, while the transmission coefficient T2 of State 2 is almost 1. This indicates that in State 1, the spin wave (magneton) can hardly pass through, while in State 2, it passes through almost completely. By switching between State 1 and State 2 using SOT, the "on" and "off" of the spin wave (magneton) can be achieved. This is a fully electrically controlled spin wave (magneton) switch based on a magneton crystal.

[0041] The magnetic crystal device proposed in this invention can be used not only as a spin wave (magneton) switch, but also as a spin wave (magneton) filter. Figure 3 This is an example of the filtering characteristics of an exemplary spin wave (magneton) filter according to the present invention. It can be observed that for spin waves (magnetons) in certain frequency ranges, the transmission coefficient T is very small, making it difficult for the spin waves (magnetons) to pass through, while spin waves (magnetons) in other frequency ranges can pass through almost completely. This can be used to construct a spin wave (magneton) filter, here a band-stop filter. Unlike the spin wave (magneton) switch described above, the implementation of the spin wave (magneton) filter only requires fixing the magneton crystal device in a certain state: State 1 or State 2. Alternatively, by switching between State 1 and State 2, the frequency band of the spin wave blocked by the filter can be changed.

[0042] It should also be understood that the spin wave switch and filter of the present invention can be used in existing current-operated circuits, and can also be applied to future magneton-operated circuits.

[0043] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to completely limit the embodiments of the invention to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize that certain variations, modifications, alterations, additions, and sub-combinations are possible based on the foregoing description and examples and embodiments.

Claims

1. A magnetic crystal device, comprising: Ferromagnetic layer; as well as An antiferromagnetic planar periodic structure is disposed on the ferromagnetic layer. Wherein, the number of periods N of the antiferromagnetic planar periodic structure is greater than 5, the width of each structural unit in the antiferromagnetic planar periodic structure is between 100 μm and 3 nm, the spacing between two adjacent structural units is also between 100 μm and 3 nm, correspondingly, the operating frequency of the magnetic crystal device is between 0.5 GHz and 1 THz, the ferromagnetic layer has a thickness of 0.5 nm to 15 nm, and the antiferromagnetic planar periodic structure has a thickness of 1 nm to 15 nm.

2. The magnetic crystal device as described in claim 1, wherein, The antiferromagnetic planar periodic structure includes: A plurality of antiferromagnetic strip-like structures extending along a first direction and periodically arranged along a second direction perpendicular to the first direction; or Multiple antiferromagnetic point structures arranged in a two-dimensional array.

3. The magnetic crystal device as described in claim 2, wherein, The antiferromagnetic strip structure has a rectangular, square, triangular, trapezoidal, or semi-circular cross-sectional shape, and the antiferromagnetic dot structure has a circular, annular, or polygonal shape.

4. The magnetic crystal device as described in claim 3, wherein, The polygon is a hollow polygon shape.

5. The magnetic crystal device as described in claim 1, further comprising: A spin Hall effect layer is disposed on the side of the ferromagnetic layer opposite to the antiferromagnetic planar periodic structure and in contact with the ferromagnetic layer. The spin Hall effect layer is used to flip the magnetic moment of the ferromagnetic layer.

6. A spin wave switch comprising the magnetic crystal device according to any one of claims 1-5.

7. The spin wave switch as described in claim 6, wherein, The frequency of the spin wave that is turned on or off by the spin wave switch is in the range of 0.5 GHz to 1 THz.

8. A spin wave filter comprising the magnetic crystal device according to any one of claims 1-5.

9. The spin wave filter as described in claim 8, wherein, The frequency of the spin wave filtered by the spin wave filter is in the range of 0.5 GHz to 1 THz.

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