Current-driven Domain Wall Motion in Artificial Magnetic Domain Structures

自旋极化电流与铁磁畴壁的相互作用在世界范围内激发了大量的实验和理论研究活动。由此产生的自旋电子器件将结合磁性和半导体材料的优势特性，并且有望快速，非易失性和多用途，能够同时存储和处理数据，同时消耗更少的能量。一种令人兴奋的自旋电子器件的新方法涉及使用自旋极化电流直接逆转感兴趣区域的磁化方向，或者“推动”其上的畴壁。后一种技术，即所谓的自旋转移转矩诱导畴壁运动，承诺以最低的开关电流密度实现最有效的器件功能。该领域的关键突出问题包括降低目前诱导壁运动所需的非常大的临界电流，以及理解传播电流驱动的畴壁的复杂行为，这两者都对自旋电子学领域的潜在应用产生了重大影响。这一合作提议为电流驱动壁运动的优化结构设计带来了一种新的方法，这也将更好地理解控制临界电流和畴壁行为的物理机制。我们的方法是使用聚焦离子束（FIB）辐照来精确控制多层膜的局部磁各向异性，并创建尺寸<=30nm的人工畴结构。通过这种方式，可以实现对壁面运动的临界电流密度以及畴结构和局部矫顽力场的精确控制。此次合作汇集了磁多层系统的FIB修正方面的专业知识，包括垂直和平面内各向异性以及互补的磁和电测量，以及强大的理论链，将解决材料结构和磁化行为中的基本物理过程。该研究的成功完成将对铁磁薄膜中的自旋传递转矩现象产生新的见解，在未来的自旋电子器件技术中具有很大的开发潜力。

The interaction of spin-polarised currents with ferromagnetic domain walls is stimulating an immense amount of experimental and theoretical research activity worldwide. The resulting spintronic devices will combine the advantageous properties of magnetic and semiconductor materials, and are expected to be fast, non-volatile and versatile, capable of simultaneous data storage and processing, while at the same time consuming less energy. An exciting new approach to spintronic devices involves using spin polarised electric currents to either directly reverse the magnetisation direction in the region of interest, or 'push' a domain wall across it. The latter technique, so-called spin transfer torque-induced domain wall motion, promises the most efficient device functionality with the lowest switching current densities. Key outstanding issues in this area include reduction of the very large critical currents presently needed to induce wall motion and understanding the complex behaviour of propagating current-driven domain walls, both of which impact strongly upon potential applications in the field of spintronics. This collaborative proposal brings a novel approach to the design of optimised structures for current-driven wall motion, which will also yield a much better understanding of the physical mechanisms that control the critical current and domain wall behaviour. Our approach is to use focussed ion beam (FIB) irradiation to precisely control the local magnetic anisotropy of multilayer films and create artificial domain structures with dimensions <=30nm. In this way exquisite control over the critical current density for wall motion, as well as the domain structure and local coercive fields, will be achieved. The collaboration brings together expertise in the FIB modification of magnetic multilayer systems with both perpendicular and in-plane anisotropy and complementary magnetic and electrical measurements, as well as a strong theoretical strand that will address fundamental physical processes in the material structuring and magnetisation behaviour. The successful completion of the proposed research will yield new insights into the phenomenon of spin transfer torque in ferromagnetic films that will have strong potential for exploitation in future spintronic device technology.