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生教育工作。该奖项将支持本科物理专业进行研究，以了解控制铁磁纳米线阵列中单个畴壁所需的过程，每个纳米线包含多个畴壁。 畴壁运动由于其有趣的物理性质以及在数据存储和传感领域的潜在应用而受到广泛关注。 然而，大部分的研究工作一直集中在一个单一的线的畴壁的行为。 这些技术的可行性取决于在大型导线阵列中操纵给定畴壁的能力。 由于系统中的每个畴壁都可能响应于驱动机制，因此需要开发技术来选择和控制给定的畴壁。PI已经确定了畴壁运动的重要特性，该特性具有改善选择性和控制的潜力。 沿主畴壁磁化方向沿着施加的局部磁场（横向场）可用于选择特定的畴壁并可靠地移动它。 由于横向场向畴壁提供额外的压力，因此横向场和整体驱动机制（其可以是外部场或由电流施加的自旋扭矩）的组合可以用于选择。 将开发新的理论来帮助解释整体行为并预测可靠的组合。 微磁模拟是这项研究的理想工具，因为该技术允许皮秒的时间分辨率与并发的纳米空间分辨率;其中每一个都是准确描绘高速磁化动力学所必需的。 该工具是访问本科生和额外的计算机编程和理论工作将结合起来，分析和理解的结果。 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。 当地的推广工作将继续与这个奖项和研究的帮助下，由PI和他的学生。 非技术性总结该奖项支持物理专业本科生对铁磁纳米线的计算和理论研究。 纳米线是一种非常微小的线，直径大约是人类头发丝的1万分之一。在磁性材料中，两个磁性相反的区域之间形成了畴壁。 当在纳米线中形成时，已经证明了其中使用畴壁的高速运动的器件：用于执行逻辑操作、用于高容量数据存储、以及作为经由变化的磁阻的传感器。 除了增加的数据存储容量外，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更快的操作速度。 这些器件将必然由多个铁磁纳米线组成，每个铁磁纳米线包含多个畴壁，但是在理解畴壁运动方面的大部分先前努力都集中在单个线中的单个畴壁上。 该奖项将用于开发技术，以控制一个单独的域墙，在其他域墙的存在，将有相互作用，通过一个单独的线在阵列中。 该项目邀请物理专业的本科生参与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，因此很容易为物理专业的本科生所理解。 学生受益于研究经验，在此过程中增加了他们在磁性材料和纳米技术的教育。一些更简单的解释和结果被用于当前的主题在入门课程，以突出经典物理学在现代研究和技术和模型的重要性已经开发出来，用于推广工作。 PI致力于为STEM领域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.