WO2018010241A1 - 一种控制自旋波传输的方法 - Google Patents

一种控制自旋波传输的方法 Download PDF

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WO2018010241A1
WO2018010241A1 PCT/CN2016/093987 CN2016093987W WO2018010241A1 WO 2018010241 A1 WO2018010241 A1 WO 2018010241A1 CN 2016093987 W CN2016093987 W CN 2016093987W WO 2018010241 A1 WO2018010241 A1 WO 2018010241A1
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spin wave
electric field
wave
spin
waveguide
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PCT/CN2016/093987
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French (fr)
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程晓敏
王升
关夏威
连晨
黄婷
缪向水
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华中科技大学
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N50/00—Galvanomagnetic devices
    • H10N50/01—Manufacture or treatment

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  • the invention belongs to the field of spintronic technology, and more particularly to a method for controlling spin wave transmission.
  • magnonics is recognized as the most promising information transmission and processing technology in the post-COMS era.
  • the information that carries information is the collective precession of electron spins, ie, spin waves rather than dissipative charge shifts.
  • magnetons quantums of spin waves
  • magnetrons information can be encoded in the amplitude and phase of the spin wave, so the effective control of the spin wave propagation becomes the core of the practical application of the magnetic vibrator.
  • a large number of logic devices based on spin wave amplitude or phase have emerged. However, so far, most of its logic functions rely on the Oersted field of current to change the spin wave dispersion relationship to achieve self-adaptation. Control of the spin wave transmission.
  • Fig. 1(a) is a typical structure for controlling the spin wave transmission by using a magnetic field, which uses the additional Oersted field generated by the current in the current-carrying line to change the magnitude of the effective bias field, thereby realizing the relationship of the spin-wave dispersion. Control to control spin wave transmission.
  • magnetic field control has some inherent drawbacks and problems: First, the generation of a local Oersted field through a current-carrying line complicates the device structure (especially in the design of a curved waveguide), while the current-carrying line continues to dissipate the system. Power will offset the low power consumption of the magnon device. Secondly, the spatial distribution non-uniformity of the local Oersted field and the stray field of adjacent waveguide branches will result in low reliability and high bit error rate of the system. Therefore, how to realize the control of spin wave transmission with high efficiency and energy saving by simple design is still a technical difficulty in the field.
  • the present invention provides an electric field-based spin wave transmission control method, which adjusts the internal exchange action intensity of the magnetic waveguide material by applying an electric field, thereby adjusting the dispersion relation of the spin wave, thereby realizing self-alignment
  • the electric field of the cyclone transmission is precisely controlled, thereby solving the technical problems of the complicated design, high energy consumption and low system reliability of the traditional magnetic field control means.
  • the present invention provides a method of electric field controlled spin wave transmission, the method comprising: applying an electric field on a spin wave waveguide structure, and changing the electric field strength can effectively change the internal exchange action intensity of the magnetic waveguide material.
  • the spin wave dispersion relation can be adjusted, and the wave number, phase velocity, wavelength and group velocity of the spin wave can be changed, thereby achieving the purpose of controlling the spin wave transmission.
  • the electric field may be introduced through a spin wave waveguide structure: a first electrode / a first insulating layer / a spin wave waveguide material / a second insulating layer / a second electrode, or a first electrode / a first insulating layer / self a whirling waveguide material/second electrode, or a first electrode/spin wave waveguide material/second insulating layer/second electrode, or a first electrode/spin wave waveguide material/second electrode, passing through the two electrodes Applying a voltage between them can introduce a normal electric field, and adjusting the voltage can change the electric field strength.
  • the electric field can be applied in any direction, but the regulation effect is most pronounced when the electric field is perpendicular to the plane of the spin wave waveguide.
  • the waveguide material may be a ferromagnetic metal element, or a ferromagnetic alloy, or a dilute magnetic semiconductor, or a magnetic insulator, or a semi-metal material, or a multi-iron material.
  • the spin wave excitation mode may be a forward volume wave (FV) or a forward volume wave (BV) or a surface wave structure.
  • FV forward volume wave
  • BV forward volume wave
  • the material is magnetized in-plane, and a bias magnetic field is applied.
  • a bias magnetic field is applied Applied perpendicular to the waveguide plane, the wave vector The direction is in the plane; in the surface wave, the bias magnetic field is applied Wave vector The directions are all in-plane and perpendicular to each other, and their group speed Phase velocity Have the same direction.
  • the Oster field control mode of current belongs to the "normally open type". During the working process of the device, the current continues to flow through the current-carrying current-carrying line to generate Joule heat; in the electric field control mode, the device belongs to the "normally-off type". "Except for the charge and discharge power consumption of the capacitor during the control state switching process, the device hardly absorbs additional power from the system. Therefore, controlling the spin wave transmission by the electric field can avoid the high energy consumption and low efficiency problems inherent in the conventional magnetic field control;
  • the electric field control can draw on the mature CMOS electric field control technology, and at the same time, it can promote the compatibility between the magnetic oscillator device and the CMOS device, and accelerate the practical process of the magnetic vibrator.
  • Fig. 1(a) is a schematic diagram showing the structure principle of a conventional Oster field controlled spin wave transmission
  • Fig. 1(b) is a schematic view showing the structure principle of an electric field controlled spin wave provided by the present invention.
  • Figure 2 is a schematic diagram of three excitation modes of spin waves: (a) reverse body wave, (b) forward body wave, and (c) surface wave.
  • FIG. 3(a) is a schematic diagram of a model of VASP simulation in Embodiment 1 of the present invention
  • FIG. 3(b) is an average potential of a model under conditions of 0.0 (black curve) and 5 V/nm (grey curve) in Embodiment 1 of the present invention. distributed.
  • Fig. 4 is a graph showing the variation of the exchange constant with the electric field intensity in the embodiment 1 of the present invention.
  • Figure 5 is a schematic diagram of a micromagnetic simulation model in Embodiment 2 of the present invention.
  • FIGS. (a)-(f) correspond to 0, 1 V/nm, 2 V/nm, 3 V/nm, 4 V/nm, and 5 V/nm, respectively.
  • Fig. 7(a) shows the surface spin wave number k and the wavelength ⁇ as a function of the electric field
  • Fig. 7(b) shows the spin wave dispersion curve (exchanged over the xy axis), and the branches from bottom to top correspond to 0, 1V. /nm, 2V/nm, 3V/nm, 4V/nm, 5V/nm.
  • the invention provides a method for controlling the spin wave transmission by an electric field.
  • the intensity of the internal exchange action of the magnetic waveguide material can be effectively changed by changing the electric field strength applied to the spin wave waveguide structure.
  • the magnitude of the exchange constant by the electric field By controlling the magnitude of the exchange constant by the electric field, the purpose of controlling the spin wave dispersion relationship and controlling the spin wave transmission can be achieved.
  • the method for regulating spin wave transmission is specifically: adjusting the spin wave dispersion relationship by applying an electric field on the spin wave waveguide structure to realize the control of the spin wave transmission.
  • the control of the spin wave transmission specifically includes: controlling the wavelength, phase velocity, wave number or group velocity of the spin wave. Specifically, increasing the voltage between the first electrode and the second electrode increases the electric field strength along the normal direction of the spin wave waveguide, and the intensity of the internal exchange action of the waveguide material is correspondingly weakened, thereby the wave number of the spin wave propagating along the waveguide. Increase, the wavelength decreases, and the phase velocity increases.
  • the electric field can be applied in any direction, but the regulation effect is most significant when the electric field is perpendicular to the plane of the spin wave waveguide.
  • the direction of the electric field applied to the spin wave waveguide structure is: normal to the spin wave waveguide plane.
  • the spin wave waveguide structure includes: a first electrode layer, a spin wave waveguide material layer, and a second electrode layer disposed in sequence.
  • the spin wave waveguide structure further includes: a first insulating layer disposed between the first electrode layer and the spin wave waveguide material layer.
  • the spin wave waveguide structure further includes: a second insulating layer disposed between the second electrode layer and the spin wave waveguide material layer.
  • the material of the spin wave waveguide material layer is a ferromagnetic metal element, a ferromagnetic alloy, a dilute magnetic semiconductor, a magnetic insulator, a semi-metal material or a multi-iron material.
  • Figure 2 shows a schematic diagram of three excitation modes of spin waves: (a) reverse body wave, (b) forward body wave, (c) surface wave; spin wave excitation mode can be reverse body wave (the forward volume wave, FV) or the forward volume wave (BV) or surface wave structure.
  • FV forward volume wave
  • BV forward volume wave
  • the material is magnetized in-plane, and a bias magnetic field is applied.
  • a bias magnetic field is applied Applied perpendicular to the waveguide plane, the wave vector The direction is in the plane; in the surface wave, the bias magnetic field is applied Wave vector
  • the directions are all in-plane and perpendicular to each other, and their group speed Phase velocity Have the same direction.
  • the first-principles calculation reveals the variation law of the exchange strength of the magnetic waveguide under the normal electric field along the waveguide plane.
  • the calculation model is shown in Figure 3(a), which is a 3-layer bcc Fe(001) atomic layer with a vacuum layer thickness of
  • the electric field along the c-axis direction is introduced by the dipole layer method, and the applied electric field intensity ranges from -5 V/nm to 5 V/nm.
  • the calculation is based on the first-principles VASP software package, and the exchange integral J is derived from the energy difference between the antiferromagnetic state and the ferromagnetic state.
  • the iron atoms in Fig. 3(a) are sequentially labeled as 1, 2, 3 from left to right.
  • the ferromagnetic energy E F and the antiferromagnetic energy E AF can be obtained as follows:
  • E F E nm -8JS 1 S 2 -8JS 2 S 3
  • E nm is the non-magnetic part of the total energy
  • J is the exchange integral
  • S i Is the total spin of the ferromagnetic (antiferromagnetic) structure atom i (in For the unit).
  • the phenomenological parameter exchange constant A can be related to the micro-parameter exchange integral J in the Heisenberg model.
  • the simulated exchange integral J, the exchange constant A, and the exchange stiffness D with the electric field change results are shown in Table 1 below.
  • the results show that the exchange constant of the three-layer Fe(001) film does change under the electric field perpendicular to the surface of the film.
  • the electric field exhibits a very significant nonlinear modulation effect on the exchange constant compared to known linear magnetoelectric effects such as electric field modulating magnetic anisotropy and electric field modulating saturation magnetization.
  • the calculated zero-field exchange constant is 1.85 ⁇ 10 -11 J/m, which is perfectly compatible with the value derived from the Curie temperature of bcc Fe (1.88 ⁇ erg/cm).
  • the exchange constant decreases rapidly. In particular, when the applied electric field intensity is 5 V/nm, the exchange constant is reduced by about 80%.
  • the influence of the electric field modulation exchange on the spin wave transmission, the change law of the spin wave wave number, the phase velocity and the wavelength are revealed by the micromagnetic simulation, and the feasibility of using the electric field control exchange constant to control the spin wave transmission is confirmed.
  • the simulation is performed using the OMMMF software package based on the LLG equation, and the calculation specifically considers the effect of the electric field modulation exchange effect:
  • M s is the saturation magnetization
  • ⁇ is the Gilbert attenuation factor
  • ⁇ is the Gilbert rotation ratio
  • Critical exchange length of iron in zero field and 5V/nm electric field The 3.1 nm and 1.3 nm are respectively, since the maximum mesh cell size is not allowed to exceed the critical exchange length, the discretization mesh size is selected to be 1 nm ⁇ 1 nm ⁇ 0.2866 nm, and a two-dimensional periodic boundary condition is applied in the xy plane.
  • Fig. 6(a-f) The spatial domain characteristics of the surface spin wave under the normal electric field are shown in Fig. 6(a-f). Obviously, the wave number increases from 0 to 5V/nm as the electric field strength increases. In other words, the phase velocity and wavelength of the surface spin wave can be changed by an applied electric field. In particular, an electric field of 5 V/nm can halve the wavelength of the spin wave compared to the zero field.
  • Fig. 7(b) is a dispersion relation curve considering the effect of the electric field modulation exchange constant. As the applied electric field strength increases, the exchange effect weakens, and the dispersion curve branches move down correspondingly in the ⁇ -k view. This will result in an increase in the wave number for a given carrier frequency.
  • Table 2 The detailed simulation calculation results are shown in Table 2.
  • the intensity of surface exchange spin wave can be effectively controlled by the applied electric field to achieve effective control of the spin wave wave number, phase velocity, wavelength and group velocity. Therefore, the applied electric field can effectively control the surface spin wave transmission. .
  • the bias magnetic field is in the plane along the x direction, and the other is the same as in the second embodiment.
  • the results show that the intensity of the exchange effect can be effectively adjusted by the applied electric field to control the dispersion relation of the reverse body wave, and the effective regulation of the spin wave number, phase velocity, wavelength and group velocity can be realized. Therefore, the applied electric field can effectively control the reverse body wave. transmission.
  • the magnetic field is applied perpendicular to the waveguide plane in the z direction, otherwise the same as in Embodiment 2.
  • the electric field to modulate the exchange intensity, the dispersion relation of the forward body wave can be effectively regulated, and the effective regulation of the spin wave number, phase velocity, wavelength and group velocity can be realized. Therefore, the applied electric field can effectively control the transmission of the forward body wave.

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Abstract

本发明公开了一种控制自旋波传输的方法，该发明属于自旋电子学领域。本方法通过在自旋波波导结构上施加电场，可以有效改变磁性波导材料内部交换作用强度。通过电场控制交换常数大小，可以达到调控自旋波色散关系进而实现控制自旋波传输的目的。本发明通过电场控制交换作用，可以超低功耗实现对自旋波传输的局部精确控制，为超低功耗、CMOS工艺流程兼容的磁振子学器件实际应用提供了可能。

Description

一种控制自旋波传输的方法 【技术领域】
本发明属于自旋电子技术领域，更具体地，涉及一种控制自旋波传输的方法。
【背景技术】
磁振子学(magnonics)以其独特的优势被公认为是后COMS时代最具潜力的信息传输和处理技术。在磁振子学中，承载信息的是电子自旋的集体进动即自旋波而非耗散性电荷移动。原理上讲，磁子(自旋波的量子)允许在不移动任何实物粒子的前提下实现信息的传输和处理，因而是没有焦耳热耗散的。在磁振子学中，信息可以编码在自旋波的振幅和相位，因而对自旋波传播的有效控制成为推进磁振子学实际应用的核心所在。近年来，涌现了一大批基于自旋波振幅或相位的逻辑器件，然而，到目前为止，其绝大多数逻辑功能实现依赖于电流的奥斯特场来改变自旋波色散关系以实现对自旋波传输的控制。
图1(a)为一种利用磁场控制自旋波传输的典型结构，其利用载流线中电流产生的附加奥斯特场改变有效偏置场的大小，从而实现对自旋波色散关系的调控以控制自旋波传输。
然而，磁场控制具有一些固有的缺陷和问题：首先，通过载流线产生局部奥斯特场将会使器件结构复杂化(特别是在弯曲波导的设计中)，而载流线持续耗散系统功率将会抵消磁振子学器件的低功耗优势。其次，局域奥斯特场的空间分布不均匀性和相邻波导分支的杂散场将会导致系统的低可靠性和高误码率。因而，如何通过简单的设计高效节能地实现自旋波传输的控制，仍然为本领域的一个技术难点。
【发明内容】
针对现有技术的以上缺陷或改进需求，本发明提供了基于电场的自旋波传输控制方法，通过施加电场，调节磁性波导材料内部交换作用强度，进而调控自旋波的色散关系，实现对自旋波传输的电场精确调控，由此解决传统磁场控制手段存在的设计复杂、高能耗和系统可靠性低下等技术问题。
为实现上述目的，本发明提供了一种电场控制自旋波传输的方法，所述方法包括，在自旋波波导结构上施加电场，通过改变电场强度可以有效改变磁性波导材料内部交换作用强度。通过电场控制交换常数大小，可以调控自旋波色散关系，改变自旋波的波数、相速、波长和群速，从而实现控制自旋波传输的目的。
优选地，所述电场可以通过自旋波波导结构引入：第一电极/第一绝缘层/自旋波波导材料/第二绝缘层/第二电极，或第一电极/第一绝缘层/自旋波波导材料/第二电极，或第一电极/自旋波波导材料/第二绝缘层/第二电极，或第一电极/自旋波波导材料/第二电极，通过在所述两电极间施加电压可以引入法向电场，调节电压可以改变电场强度。理论上，电场可以沿任意方向施加，但当电场垂直于自旋波波导平面时调控效应最为显著。
具体地，增大第一电极和第二电极间电压，沿自旋波波导平面法向的电场强度随之增大，波导材料内部交换作用强度相应减弱，从而沿波导传播的自旋波的波数增大，波长减小，相速增大。换言之，自旋波的传播参数随电场强度变化而单调变化，这种电场调控效应可以用于实现对自旋波传输的控制。
优选地，所述波导材料可以是铁磁金属单质，或铁磁合金，或稀磁半导体，或磁性绝缘体，或半金属材料，或多铁材料。
优选地，所述自旋波激发模式可以是反向体波(the forward volume wave，FV)或前向体波(the backward volume wave，BV)或表面波(surface  wave)结构。具体而言，反向体波中，材料沿面内磁化，且外加偏置磁场
Figure PCTCN2016093987-appb-000001
平行于波矢
Figure PCTCN2016093987-appb-000002
前向体波中，外加偏置磁场
Figure PCTCN2016093987-appb-000003
垂直于波导平面施加，波矢
Figure PCTCN2016093987-appb-000004
方向在面内；表面波中，外加偏置磁场
Figure PCTCN2016093987-appb-000005
和波矢
Figure PCTCN2016093987-appb-000006
方向均在面内且互相垂直，其群速度
Figure PCTCN2016093987-appb-000007
和相速度
Figure PCTCN2016093987-appb-000008
具有相同的方向。
总体而言，通过本发明所构思的以上技术方案与现有技术相比，具有以下有益效果：
(1)电流的奥斯特场控制方式属于“常开型”，在器件工作过程中，电流持续流过产生磁场的载流线产生焦耳热；而在电场控制模式中器件属于“常关型”，除去控制状态切换过程中的电容充放电功耗，器件几乎不从系统吸收额外功耗。因而通过电场控制自旋波传输可以规避传统磁场控制所固有的高能耗、低功效问题；
(2)通过平行板电容器引入电场可以适应复杂的波导形状设计需求，获得全局均一的控制，亦可实现局部精确控制；而在传统磁场控制中电流的奥斯特场的空间分布具有非均匀性，而且相邻控制磁场间易产生相互串扰。因而采用电场控制大大减小了磁振子学器件设计的复杂度；
(3)采用电场控制可以借鉴成熟的CMOS电场控制技术，同时可以促进磁振子学器件与CMOS器件的兼容性，加速推进磁振子学的实用化进程。
【附图说明】
图1(a)为传统的奥斯特场控制自旋波传输的结构原理示意图，图1(b)为本发明提供的电场控制自旋波的结构原理示意图。
图2是自旋波的三种激发模式原理示意图：(a)反向体波，(b)前向体波，(c)表面波。
图3(a)为本发明实施例1中VASP模拟的模型原理图，图3(b)为本发明实施例1中模型在0.0(黑色曲线)和5V/nm(灰色曲线)条件下面平均电势分布。
图4为本发明实施例1中交换常数随电场强度变化曲线。
图5为本发明实施例2中微磁模拟模型原理图。
图6为本发明实施例2中自旋波的空间域特性，图(a)-(f)分别对应0，1V/nm，2V/nm，3V/nm，4V/nm，5V/nm。
图7(a)为表面自旋波波数k和波长λ随电场变化曲线，图7(b)为自旋波色散关系曲线(交换过xy轴)，从下到上各分支依次对应0，1V/nm，2V/nm，3V/nm，4V/nm，5V/nm情形。
【具体实施方式】
为了使本发明的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。此外，下面所描述的本发明各个实施方式中所涉及到的技术特征只要彼此之间未构成冲突就可以相互组合。
本发明提供了一种电场控制自旋波传输的方法，通过改变施加在自旋波波导结构上的电场强度可以有效改变磁性波导材料内部交换作用强度。通过电场控制交换常数大小，可以达到调控自旋波色散关系进而实现控制自旋波传输的目的。
本发明提供的调控自旋波传输的方法具体为：通过在自旋波波导结构上施加电场来调控自旋波色散关系，实现对自旋波传输的控制。
其中，对自旋波传输的控制具体包括：对自旋波的波长、相速、波数或群速度的控制。具体地，增大第一电极和第二电极间电压，沿自旋波波导平面法向的电场强度随之增大，波导材料内部交换作用强度相应减弱，从而沿波导传播的自旋波的波数增大，波长减小，相速增大。
在本发明实施例中，电场可以沿任意方向施加，但当电场垂直于自旋波波导平面时调控效应最为显著。优选地，施加在所述自旋波波导结构上的所述电场的方向为：沿自旋波波导平面法向。
在本发明实施例中，自旋波波导结构包括：依次设置的第一电极层、自旋波波导材料层和第二电极层。
作为本发明的一个实施例，自旋波波导结构还包括：设置在所述第一电极层与所述自旋波波导材料层之间的第一绝缘层。
作为本发明的一个实施例，如图1(b)所示，自旋波波导结构还包括：设置在所述第二电极层与所述自旋波波导材料层之间的第二绝缘层。
其中，自旋波波导材料层的材料为铁磁金属单质、铁磁合金、稀磁半导体、磁性绝缘体、半金属材料或多铁材料。
图2示出了，自旋波的三种激发模式原理示意图：(a)反向体波，(b)前向体波，(c)表面波；自旋波激发模式可以是反向体波(the forward volume wave，FV)或前向体波(the backward volume wave，BV)或表面波(surface wave)结构。具体而言，反向体波中，材料沿面内磁化，且外加偏置磁场
Figure PCTCN2016093987-appb-000009
平行于波矢
Figure PCTCN2016093987-appb-000010
前向体波中，外加偏置磁场
Figure PCTCN2016093987-appb-000011
垂直于波导平面施加，波矢
Figure PCTCN2016093987-appb-000012
方向在面内；表面波中，外加偏置磁场
Figure PCTCN2016093987-appb-000013
和波矢
Figure PCTCN2016093987-appb-000014
方向均在面内且互相垂直，其群速度
Figure PCTCN2016093987-appb-000015
和相速度
Figure PCTCN2016093987-appb-000016
具有相同的方向。
下面通过具体实施例的阐述，以进一步说明本发明实质性特点和显著的进步，但本发明绝非仅限于实施例。
实施例1
本实施例通过第一性原理计算揭示了磁性波导在沿波导平面法向电场作用下交换作用强度变化规律。
计算采用模型如图3(a)所示，为3层bcc Fe(001)原子层，其真空层厚度为
Figure PCTCN2016093987-appb-000017
沿c轴方向的电场通过偶极层方法引入，施加电场强度范围为-5V/nm到5V/nm。计算基于第一性原理VASP软件包进行，交换积分J通过反铁磁态和铁磁态的能量差推导得出。
为简化描述，将图3(a)中铁原子从左到右依次标记为1，2，3。仅 考虑最近邻交换作用，可以得到铁磁态能量EF和反铁磁态能量EAF分别为：
EF＝Enm-8JS1S2-8JS2S3
Figure PCTCN2016093987-appb-000018
其中Enm为总能量的非磁性部分，J是交换积分，Si
Figure PCTCN2016093987-appb-000019
是铁磁态(反铁磁态)结构原子i的总自旋(以
Figure PCTCN2016093987-appb-000020
为单位)。
由上述两式可得，交换积分的表达式
Figure PCTCN2016093987-appb-000021
唯象参数交换常数A可以通过以下公式与海森堡模型中微观参数交换积分J建立联系，对于体心立方结构A＝2JS2/a；其中a为晶格常数，交换劲度D为D＝2JSa2；模拟所得交换积分J，交换常数A，交换劲度D随电场变化结果如下表1所示。
表1
Figure PCTCN2016093987-appb-000022
如图4中第一性原理计算结果所示，结果表明，3层Fe(001)薄膜的交换常数在垂直于薄膜表面的电场作用下确实发生了变化。相比于已知的线性磁电效应例如电场调制磁各向异性、电场调制饱和磁化强度，电场对交换常数表现出十分明显非线性调制作用。具体而言，计算所得零场交换常数为1.85×10-11J/m，与从bcc Fe的居里温度推导所得值(1.88μerg/cm) 完美契合。随着外加电场强度的增加，交换常数快速减小。特别地，当外加电场强度为5V/nm时，交换常数减小了约80％。
由此说明，通过外加电场实现对交换作用强度的调制是可行的，而且交换常数的电场调制效应是十分显著的。
实施例2
本实施例通过微磁模拟揭示了电场调制交换作用对自旋波传输的影响，自旋波波数、相速、波长相应的变化规律，证实利用电场调控交换常数控制自旋波传输的可行性。
模拟采用基于LLG方程的OOMMF软件包进行，计算特别考虑了电场调制交换作用效应：
Figure PCTCN2016093987-appb-000023
其中
Figure PCTCN2016093987-appb-000024
为归一化磁化矢量，Ms为饱和磁化强度，α为吉尔伯特衰减因子，γ为吉尔伯特旋磁比。
Figure PCTCN2016093987-appb-000025
为有效场，包括海森堡交换场，磁各向异性场，退磁场和外加偏置磁场，可以表示为：
Figure PCTCN2016093987-appb-000026
其中交换常数
Figure PCTCN2016093987-appb-000027
是电场依赖的。计算采用的模型如图5所示，模拟了电场对表面波传输的影响，其中波导为500×500×0.2866nm3的薄膜平面波导，沿y轴方向施加偏置磁场大小μ0H0＝1T，角频率为4×1011rad/s的正弦微波源用于激发沿x方向传播的表面波，模拟采用了Fe的典型参数值：
(1)饱和磁化强度MS＝1.75×106A/m；
(2)吉尔伯特衰减因子α＝0.03；
(3)吉尔伯特旋磁比γ＝2.211×105m/(A·s)；
(4)各向异性常数K＝0(忽略了立方晶系Fe相对较小的磁各向异性能)。
零场和5V/nm电场下铁的临界交换长度
Figure PCTCN2016093987-appb-000028
分别为3.1nm和1.3nm，由于最大网格单元尺寸不允许超过临界交换长度，离散化网格尺寸选为1nm×1nm×0.2866nm，并且在xy平面内应用了二维周期性边界条件。
法向电场作用下表面自旋波的空间域特性如图6(a-f)所示，显然随着电场强度从0增加到5V/nm波数相应有所增加。换言之，表面自旋波的相速和波长可以通过外加电场改变。特别地，相比于零场，5V/nm的电场可以将自旋波波长减半。
考虑交换作用后，在有限尺寸铁磁薄膜内表面自旋波色散关系的解析形式为
Figure PCTCN2016093987-appb-000029
其中ωex＝ω0+λexωMk2，ω0＝γμ0H0，ωM＝γμ0Ms，
Figure PCTCN2016093987-appb-000030
d为薄膜厚度。图7(b)为考虑了电场调制交换常数效应后的色散关系曲线。随着外加电场强度增加，交换作用减弱，在ω-k视图中色散曲线分支相应下移。对于给定的载波频率，这将导致波数增加。详细的模拟计算结果如表2所示。
表2
电场强度(V/nm) λ(nm) k(×109rad/m) kth(×109rad/m)
0 45.170 0.139 0.139
±1 44.768 0.140 0.141
±2 43.300 0.145 0.148
±3 38.217 0.164 0.164
±4 29.967 0.210 0.199
±5 19.621 0.320 0.313
由此说明，通过外加电场调制交换作用强度可以有效调控表面自旋波色散关系，实现对自旋波波数、相速、波长和群速的有效调控，因而外加电场可以有效控制表面自旋波传输。
实施例3
偏置磁场在面内沿x方向，其它同实施例2。结果表明，通过外加电场调制交换作用强度可以有效调控反向体波的色散关系，实现对自旋波波数、相速、波长和群速的有效调控，因而外加电场可以有效控制反向体波的传输。
实施例4
磁场垂直于波导平面沿z方向施加，其它同实施例2。，通过外加电场调制交换作用强度可以有效调控前向体波的色散关系，实现对自旋波波数、相速、波长和群速的有效调控，因而外加电场可以有效控制前向体波的传输。
本领域的技术人员容易理解，以上所述仅为本发明的较佳实施例而已，并不用以限制本发明，凡在本发明的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本发明的保护范围之内。

Claims (9)

  1. 一种控制自旋波传输的方法，其特征在于，通过在自旋波波导结构上施加电场来调控自旋波色散关系，实现对自旋波传输的控制。
  2. 如权利要求1所述的方法，其特征在于，所述对自旋波传输的控制具体包括：对自旋波的波长、相速、波数或群速度的控制。
  3. 如权利要求1所述的方法，其特征在于，施加在所述自旋波波导结构上的所述电场的方向为：沿自旋波波导平面法向。
  4. 如权利要求1-3任一项所述的方法，其特征在于，所述自旋波波导结构包括：依次设置的第一电极层、自旋波波导材料层和第二电极层。
  5. 如权利要求4所述的方法，其特征在于，所述自旋波波导结构还包括：设置在所述第一电极层与所述自旋波波导材料层之间的第一绝缘层。
  6. 如权利要求4或5所述的方法，其特征在于，所述自旋波波导结构还包括：设置在所述第二电极层与所述自旋波波导材料层之间的第二绝缘层。
  7. 如权利要求1所述的方法，其特征在于，所述施加电场会改变波导材料内部的交换作用强度，从而改变自旋波色散关系，实现对自旋波传输的控制。
  8. 如权利要求4-7任一项所述的方法，其特征在于，所述自旋波波导材料层的材料为铁磁金属单质、铁磁合金、稀磁半导体、磁性绝缘体、半金属材料或多铁材料。
  9. 如权利要求1-8任一项所述的方法，其特征在于，自旋波的激发方式为前向体波模式、反向体波模式或表面波模式。
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