兰州大学机构库 >物理科学与技术学院
磁斯格明子动力学的微磁学模拟研究
Alternative TitleDynamic of magnetic skyrmion using micromagnetic simulations
夏海艳
Subtype博士
Thesis Advisor王建波
2020-05-30
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name理学博士
Degree Discipline凝聚态物理
Keyword斯格明子 电压调控磁各向异性 钉扎/脱钉扎 反铁磁材料
Abstract磁斯格明子(magnetic skyrmion)是一种具有准粒子特性的拓扑自旋结构。 这种新型的磁自旋结构由于空间尺寸较小和驱动其运动的临界电流密度较低, 在下一代信息存储器和自旋电子学器件中有很大的应用潜力,如赛道存储器、 微波探测器、逻辑门器件和自旋纳米振荡器等。有效可控地操纵skyrmion运动 无论在理论研究方面还是在实际应用上都具有非常重要的物理意义。鉴于此, 本论文主要采用微磁学模拟,尝试用多种方法调控skyrmion运动,并结合理论 模型分析了模拟结果。论文的主要内容如下: 首先,我们研究磁各向异性梯度对skyrmion运动的影响。通过在电极/磁性 多层膜/斜坡绝缘层/电极结构中利用电压调控磁各向异性效应,在磁性层中产生 磁各向异性梯度。结果发现,该磁各向异性梯度能够驱动skyrmion在磁性纳米 条带中运动。随着磁各向异性梯度从-1.0×1010 J/m4增大到-8.0×1010 J/m4, skyrmion运动速度从 0.1 m/s增大到 23 m/s。磁各向异性梯度和平面内外磁场可 以共同有效地调控skyrmion的运动方向和运动速度skyrmion运动速度与磁性材 料的阻尼系数成反比。基于Thiele方法,建立理论分析模型,其分析结果与微磁 学模拟相吻合。 其次,我们研究了磁性纳米带中槽口对 2&piskyrmion 钉扎/脱钉扎作用的影 响。结果表明凸槽口/凹槽口在磁性纳米带中分别能够产生能量势阱和能量势垒, 其能量势阱和能量势垒主要来源于退磁能和 DMI 能量。从能量的角度,凸槽口 /凹槽口均可以作为 2&piskyrmion钉扎点。为了研究 2&piskyrmion钉扎/脱钉扎的动 态过程,我们采用自旋波驱动 2&piskyrmion运动。结果表明槽口类型,深度以及 自旋波激发磁场频率和振幅对 2&piskyrmion动态钉扎过程均有影响。 另外,我们研究了局域磁场对 2&piskyrmion 钉扎/脱钉扎作用。我们先研究 了反铁磁材料对 2&piskyrmion 钉扎/脱钉扎作用。由于反铁磁材料在 AFM/FM 交 界处能够诱导交换偏置场,从而使得 AFM/FM 交界区域可以作为钉扎点,其钉 扎强度依赖于交换偏置场强度。反铁磁材料诱导的交换偏置场在磁性纳米带中 可以产生能量势垒或势阱,其能量势垒或势阱主要来源于退磁能,DMI 能量和 交换偏置能。然后我们研究了磁性圆盘对 2&piskyrmion 钉扎/脱钉扎的影响。研 究表明磁性圆盘能够在磁性纳米条带中产生能量势阱,从而可以作为 2&piskyrmion钉扎点,其钉扎强度依赖于磁性圆盘直径。 最后,我们采用微磁学模拟方法,首先研究了用电操控反铁磁 skyrmion 的 写入,驱动以及读取过程。其次,基于 Y-性纳米结构,我们实现了反铁磁 skyrmion 的复制,删除,或门和与门的功能性操控。其功能性操控时间为皮秒 量级,有利于快速信息处理。实现该功能性操控的关键点在于 Y-型纳米结构。 在合适的 Y-型纳米结构中,skyrmion 和畴壁以可控地方式在纳米带中运动,而 不会出现不理想的畴壁钉扎、消失甚至新畴壁的成核。最后,我们研究了反铁 磁 skyrmion 链的运动。在一定范围内的电流密度作用下,skyrmion 链的运动速 度与电流密度成正比。
Other AbstractMagnetic skyrmions are topological spin texures, which possess great potential applications in next-generation spintronics, such as racetrack memory, microwave detector, logic gates and neuromorphological device. Controllable manipulation of skyrmion motion is fundamental to understanding the physics of skyrmions and their potential applications in spintronic devices. In this work, we investigated controllable manipulation of skyrmion in ferriomagnetic manterials and antiferriomagnetic materials using micromagnetic simulation. The main research contents of this paper are as follows: Firstly, we investigated skyrmion motion induced by the gradient of voltagecontrolled magnetic anisotropy (VCMA). Simulations show that the VCMA gradient can induce the skyrmion into a steady motion along the magnetic strip without reflection. The velocity of magnetic skyrmion lineally increases from 0.1 m/s to 23 m/s with the VCMA gradientincreasing from -1.0×1010 J/m4 to -8.0×1010 J/m4. The skyrmion velocity is inverse proportion to the damping factor. Furthermore, both the direction and velocity of skymion motion can be modulated by the VCMA gradient and in-plane filed. An analytical model based on the Thiele theory was derived, which was well in agreement with the simulation results. Secondly, the 2&piskyrmion pinning by constrictions and protrusions in racetrack was investigated. The simulations demonstrated that energy barriers or energy wells are generated by constrictions and protrusions due to the demagnetizing and DMI. From the energy point of view, both types of constrictions and protrusions were found to act as pinning centers for 2&piskyrmion. Spin waves were employed to induce 2&piskyrmion motion to study the dynamics of the 2&pi-skyrmion pinning. The simulations showed that the pinning/depinning of 2&pi-skyrmion exhibits dependence on the type and depth of constrictions and protrusions, as well as the frequency and amplitude of the oscillating magnetic field for exciting spin waves. Thirdly, the influence of the local magnetic field on the pinning/depinning behavior of 2&piskyrmions was investigated. Firstly, we investigated the influence of AFM materials on the pinning/depinning of 2&piskyrmion. The AFM nanowires can induce exchange bias field at the AFM/FM crossing areas, which can act as pinning sites. The strength of pinning depends on the exchange bias field. The interaction mechanism between the exchange bias and 2&piskyrmion was studied from the energy point of view. Energy barriers or energy wells are generated at the AFM/FM crossing area due to the demagnetizing, DMI and exchange bias energy. Secondly, the effect of the local magnetic disk on the pinning/depinning behavior of 2&piskyrmions was studied. Simulation results demonstrate that the magnetic disk can generate energy wells and then can serve as the pinning sites for 2&piskyrmion. The strength of pinning depends on the diameter of the local magnetic disk. Finally, the electrical writing, driving and reading of AFM skyrmions were realized. Furthermore, duplication and deletion of skyrmions, logical OR and AND function were designed in AFM materials with a cusp or smooth Y-junction structures. The operational time is in dozens of picoseconds, enabling ultrafast information processing. Key factor for the successful operation is the relatively complex Yjunction structures, where domain walls propagate in a controlled manner, without significant risk of pinning, vanishing or unwanted depinning of existing domain walls as well as nucleation of new domain walls. The motion of AFM skyrmion chain in racetrack was also investigated. The AFM skyrmion chain velocity, independent of the skyrmions number of each skyrmion-chain, is in proportion to the current density.
Pages128
URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/465087
Collection物理科学与技术学院
Affiliation
物理科学与技术学院
Recommended Citation
GB/T 7714
夏海艳. 磁斯格明子动力学的微磁学模拟研究[D]. 兰州. 兰州大学,2020.
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