Magnetic Rings for Memory and Logic Devices

本计画将研究介观磁环的特性，并探讨其在记忆体或逻辑元件等磁性元件上的应用。直径在200 nm及以上的薄膜磁环可以在几种不同的状态下磁化。例如，磁化可以围绕环周向地定向（"涡旋"状态），或者环可以在直径的相对端处包含两个迎面的壁（"洋葱"状态）。最近，观察到另一种状态（“扭曲”状态），它由包含360度壁的涡旋状态组成。环可以在这些状态之间可重复地切换，从而引入了环可能成为磁数据存储或数据处理设备的候选者的可能性。在这个项目中，将使用电子束光刻结合离子束溅射来制造圆形和椭圆形环。环将由单磁层，交换偏置层和自旋阀多层。它们的磁状态将被确定为几何形状的函数。特别是稳定性的旋涡，洋葱和扭曲的磁化状态，周围的环移动壁的可能性，和钉扎的墙壁将被检查。微磁模型将用于帮助解释观测结果。在小环上的磁阻测量将通过在两级光刻工艺中使环电接触来进行。基于这些结果，我们将设计出一个磁性随机存取存储器单元的原型，在这个单元中，数据位以不同的磁化状态存储在环中。位将通过施加场来写入，并使用磁阻来读回。设计一个磁逻辑门的可能性也将被评估，其中数据位（由域配置表示）可以被写入，操纵和读回。 将结合这些研究活动开展教育和交流活动。这将包括两名研究生和几名本科生参与研究，将研究成果纳入教学，以及继续开展一系列当地学校外展活动。此外，还将设计适合高中或大学一年级学生的软件工具，该软件工具将说明磁场，磁通密度和磁化，并允许学生探索磁滞现象，提高他们对磁性材料和器件的理解。

In this project, the properties of mesoscopic magnetic rings will be investigated, and their utility in magnetic devices such as memory or logic cells will be explored. Thin-film magnetic rings, with diameters of 200 nm and above, can be magnetized in several distinct states. For example the magnetization can be oriented circumferentially around the ring (a 'vortex' state), or the ring can contain two head-on walls at opposite ends of a diameter (an 'onion' state). Recently, another state (a 'twisted' state) was observed which consists of a vortex state containing a 360 wall. Rings can be reproducibly switched between these states, introducing the possibility that rings could be candidates for magnetic data storage or data manipulation devices. In this project, circular and elliptical rings will be fabricated using electron-beam lithography combined with ion-beam sputtering. Rings will be made from single magnetic layers, exchange-biased layers and spin-valve multilayers. Their magnetic states will be determined as a function of geometry. In particular the stability of the vortex, onion and twisted magnetization states, the possibility of moving walls around the ring, and pinning of the walls will be examined. Micromagnetic modeling will be used to help interpret the observations. Magnetoresistance measurements on small rings will be made by electrically contacting the rings in a two-level lithography process. Based on the results, a magnetic random access memory cell will be prototyped, in which data bits are stored in the ring as different magnetization states. Bits will be written by applying a field and read back using magnetoresistance. The possibility of designing a magnetic logic gate will also be assessed, in which data bits (represented by domain configurations) can be written, manipulated, and read back. Education and communication activities will be carried out in combination with these research activities. These will include the participation in research of two graduate and several undergraduate students, the incorporation of research findings into teaching, and the continued development of a series of local school outreach activities. In addition, a software tool will be designed suitable for senior high school or freshman college students, which will illustrate magnetic fields, flux density and magnetization, and allow students to explore hysteresis phenomena, improving their understanding of magnetic materials and devices.