Magnetic Rings for Memory and Logic Devices

在本项目中，将研究介观磁环的性质，并探索其在存储器或逻辑单元等磁性器件中的应用。直径在200 nm以上的薄膜磁环可以在几种不同的状态下被磁化。例如，磁化可以围绕环的圆周方向定向(“漩涡”状态)，或者环可以在直径的相反两端包含两个迎面壁(“洋葱”状态)。最近，观察到了另一种状态(扭曲状态)，它由一个包含360度壁的涡旋态组成。环可以在这些状态之间重复切换，从而使环有可能成为磁性数据存储或数据处理设备的候选。在这个项目中，将使用电子束光刻和离子束溅射相结合的方法来制造圆形和椭圆形环。环将由单磁性层、交换偏置层和自旋阀多层膜制成。它们的磁态将作为几何的函数来确定。特别是涡旋、洋葱和扭曲磁化态的稳定性，环周围移动壁的可能性，以及壁的钉扎。微磁模型将被用来帮助解释观测结果。在两级光刻工艺中，将通过电接触环来测量小环上的磁阻。基于这些结果，将制作磁随机存取存储单元的原型，其中数据比特以不同的磁化状态存储在环中。将通过施加一个场来写入位，并使用磁阻回读。还将评估设计磁逻辑门的可能性，其中可以写入、操纵和回读数据比特(由域配置表示)。将结合这些研究活动开展教育和交流活动。这些措施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本地学校外展活动。此外，还将设计一个适合高中生或大学一年级学生使用的软件工具，该工具将说明磁场、磁通密度和磁化强度，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.