Micromagnetic Study of Controllable Domain Wall Motion in Ferromagnetic Nanowire Arrays via Transverse Magnetic Fields

该奖项支持铁磁材料和磁化动力学的理论和计算研究以及本科教育工作。该奖项将支持物理学专业的本科生进行研究，以了解控制铁磁纳米线阵列中单个畴壁的必要过程，每个铁磁纳米线都包含多个畴壁。由于各种有趣的物理性质和在数据存储和传感方面的潜在应用，畴壁运动正受到广泛的研究。然而，大部分的研究工作都集中在单线中一个畴壁的行为上。这里的技术的可行性取决于在大型电线阵列中操纵给定域壁的能力。由于系统中的每个域壁都可能响应驱动机制，因此需要开发技术来选择和控制给定的域壁。PI已经确定了畴壁运动的一个重要特征，该特征具有改善选择性和控制的潜力。沿主畴壁磁化方向施加的局部磁场，即横向磁场，可以用来选择特定的畴壁并可靠地移动它。由于横向场对畴壁产生额外的压力，因此可以选择横向场与整体驱动机构的组合，驱动机构可以是外场，也可以是电流施加的自旋力矩。新的理论将被开发出来，以帮助解释整体行为和预测可靠的组合。微磁模拟是这项研究的理想工具，因为该技术允许皮秒时间分辨率与并发纳米空间分辨率；每一个都是准确描述高速磁化动力学所必需的。该工具可供本科生使用，并且将结合额外的计算机编程和理论工作来分析和理解结果。PI和马奎特大学致力于鼓励STEM领域代表性不足的群体参与研究。在这个奖项的帮助下，当地的推广工作将继续进行，并由PI和他的学生进行研究。本奖项支持物理专业本科学生对铁磁纳米线进行计算和理论研究。纳米线是一种非常微小的金属线，直径比人的头发还小1万倍。在磁性材料中，畴壁在两个方向相反的磁性区域之间形成。当在纳米线中形成时，已经证明了器件中使用畴壁的高速运动：执行逻辑运算，用于高容量数据存储，并通过改变磁电阻作为传感器。除了增加数据存储容量之外，磁性设备是非易失性的，消耗更少的能量，并且具有比当今技术快得多的操作速度。这些器件必须由多个铁磁纳米线组成，每个纳米线都包含多个畴壁，但大多数先前在理解畴壁运动方面的努力都集中在单线中的单个畴壁上。该合同将用于开发控制单个域墙的技术，在其他域墙存在的情况下，通过阵列中的单个电线与其他域墙进行交互。本项目由物理专业本科学生参与，进行计算机模拟和理论建模。计算机模拟遵循纳米线中每个微小磁性区域的运动方程。运动方程本质上是一个扭矩方程，因此对于物理专业的本科生来说很容易理解。学生从研究经验中受益，这一过程增加了他们在磁性材料和纳米技术方面的教育。一些较简单的解释和结果用于介绍性课程的当前主题，以突出经典物理学在现代研究和技术中的重要性，并开发了用于推广工作的模型。PI致力于为STEM领域中代表性不足的学生提供机会。

TECHNICAL SUMMARYThis award supports theoretical and computational research and undergraduate education efforts on ferromagnetic materials and magnetization dynamics.Undergraduate physics majors will be supported by this award to conduct research on understanding the processes necessary to control a single domain wall in an array of ferromagnetic nanowires each of which contain multiple domain walls. Domain wall motion is being intensely investigated due to a variety of interesting physical properties and potential applications in data storage and sensing. However the bulk of the research efforts have been focused on the behavior of one domain wall in a single wire. The viability of the technologies here depends on the ability to manipulate a given domain wall in large arrays of wires. Since each domain wall in the system potentially responds to the driving mechanism, techniques need to be developed to select and control a given domain wall.The PI has identified an important characteristic of domain wall motion which has the potential for improving selectivity and control. Local magnetic fields applied along the primary domain wall magnetization direction, a transverse field, can be used to select a particular domain wall and to move it reliably. Because the transverse field gives additional pressure to a domain wall the combination of the transverse field and the overall driving mechanism, which could be an external field or a spin-torque applied by a current, can be used for selection. New theories will be developed to assist in explaining the overall behavior and predict reliable combinations. Micromagnetic simulation is an ideal tool for this research as the technique allows for picosecond time resolution with concurrent nanometer spatial resolution; each of which is necessary for accurately depicting the high speed magnetization dynamics. The tool is accessible to undergraduates and additional computer programming and theoretical efforts will be combined to analyze and understand the results. The PI and Marquette University are committed to encouraging underrepresented groups in the STEM fields to participate in research. Local outreach efforts will be continued with the help of this award and research by the PI and his students. NONTECHNICAL SUMMARYThis award supports computational and theoretical research on ferromagnetic nanowires by undergraduate physics majors. Nanowires are very tiny wires that are some 10,000 times smaller in diameter than a human hair.In a magnetic material a domain wall forms between two regions of oppositely oriented magnetism. When formed in a nanowire, devices have been demonstrated in which the high- speed motion of a domain wall is used: to carry out logic operations, for high capacity data storage, and as sensors via varying magnetoresistance. In addition to increased data storage capacity, magnetic devices are non-volatile, consume less energy, and have operational speeds significantly faster than today's technologies. These devices will necessarily consist of multiple ferromagnetic nanowires each containing multiple domain walls, but the majority of the prior effort in understanding domain wall motion has focused on single domain walls in a single wire. This award will be used to develop techniques to control an individual domain wall, in the presence of other domain walls with which there will be interactions, through an individual wire in the array. The project engages undergraduate physics majors to participate in carrying out computer simulations and theoretical modeling. The computer simulations follow an equation of motion for each tiny magnetic region in the nanowire. The equation of motion is essentially a torque equation and as such is easily accessible to undergraduate physics majors. Students benefit from the research experience which in the process adds to their education in magnetic materials and nanotechnology. Some of the simpler interpretations and results are used for current topics in introductory courses to highlight the importance of classical physics in modern research and technology and models have been developed to use in outreach efforts. The PI is committed to providing opportunities for students underrepresented in the STEM fields.