Writing nanomagnets: Investigation of new magnetic nanostructures fabricated by focussed electron and ion beams

本奖学金的目的是研究通过聚焦电子和离子束沉积（FEBID/FIBID）制备的新型纳米磁性材料，这对自旋电子学应用具有巨大的技术兴趣。纳米磁铁是具有纳米尺寸的磁性系统，即它们仅由几个原子沿其长度，宽度和/或厚度形成。由于它们的尺寸与控制其性质的基本长度相同，它们的行为与宏观磁体不同，这使得它们在许多应用中得到开发成为可能。特别是，新型纳米磁铁的开发是过去几十年计算机性能大幅提高的关键因素之一，因为硬盘驱动器的存储和传感部分都是由这种纳米结构形成的。为了使计算性能继续呈指数级增长，新技术应该包括更大的小型化、更高的速度和更低的功耗。自旋电子学是利用纳米磁体中的新物理现象来存储和处理信息的电子学领域，一些自旋电子器件，如stt - mram或赛道存储器已被提出作为CMOS技术的有前途的替代品。然而，很明显，为了对计算产生革命性的影响，自旋电子学需要新的方法来制造磁性纳米结构。目前用于纳米级磁性系统的标准工艺是基于使用物理方法的薄膜沉积和使用掩膜和抗蚀剂的光刻技术；这些自上而下的方法面临着它们的物理限制，RAM和CPU操作完全由晶体管技术主导。因此，迫切需要研究使用自下而上方法的更先进的制造技术，其中分子作为制造功能纳米材料的基石。在这个项目中使用的技术（FEBID/FIBID）是直接书写纳米光刻技术，基于与高能聚焦电子束或离子束（SEM或FIB）相互作用而吸附在衬底上的气体分子的局部化学气相沉积。这些超高分辨率的快速处理技术非常灵活，不需要掩模或电阻。具体来说，它们具有在任何表面上制造复杂三维纳米结构的独特能力。当使用这些工艺时，通常发现的主要缺点是，由于分子在聚焦光束下的分解效率较差，沉积的材料是来自前体气体分子的元素的混合物，具有与所追求的特性相去甚远的特性。然而，磁性材料是这种负面情况的例外，因为在适当的生长条件下，使用3d铁磁性金属的羰基，可以直接沉积纯磁性材料。由于这些技术的诞生，以前使用磁性材料的FEBID/FIBID的结果主要用于研究沉积物的纯度，并复制以前通过标准图图化技术获得的结果。该项目将进一步开发FE/IBID在磁性纳米结构制造方面的独特能力。通过改变沉积条件，我们将研究一套新的纳米磁性材料，其微观结构和组成将被控制在纳米尺度上。通过结合气体前驱体和聚焦光束，可以制造出不同类型的磁性化合物，以及多层纳米结构。此外，复杂三维纳米磁体的发展将创造出第一个可以在所有三个方向上存储和处理磁性信息的设备。为了描述这些系统的特征，将结合磁、结构和光谱技术以及磁成像和模拟技术。

The objective of this fellowship is the investigation of new nanomagnetic materials fabricated by focussed electron and ion beam deposition (FEBID/FIBID), which has a huge technological interest for spintronic applications. Nanomagnets are magnetic systems with nanometric dimensions, i.e. they are formed just by a few atoms along their length, width and/or thickness. Because their dimensions become of the order of the fundamental lengths governing their properties, they behave differently from macroscopic magnets, which has made possible their exploitation in many applications. In particular, the development of new types of nanomagnets is one of the key ingredients for the vast increase in computer performance during the last decades, since both storage and sensing part of hard disk drives are formed by this type of nanostructures. In order to continue the exponential increase in computing performance, new technologies should involve greater miniaturisation, higher speeds and lower power consumption. Spintronics is the area of electronics which exploits new physical phenomena in nanomagnets to store and process information, and some spintronic devices such as STT-MRAMs or racetrack memories have been proposed as promising alternatives to CMOS technology. However, it is clear that in order to have a revolutionary impact in computing, spintronics needs of new ways to fabricate magnetic nanostructures. Standard processes used now to pattern magnetic systems at the nanoscale are based on thin film deposition using physical methods and lithography techniques using masks and resists; these top-down methods are facing their physical limits and RAM and CPU operations are fully dominated by transistor technology. It is therefore urgently needed to study more advanced fabrication techniques which use bottom-up approaches, where molecules serve as building blocks for the fabrication of functional nanomaterials.The techniques to be used in this project, (FEBID/FIBID) are direct-writing nanolithography techniques based on the local chemical vapour deposition of gas molecules adsorbed on a substrate as a result of the interaction with high energy focussed beams of electrons or ions (SEM or FIB). These ultra-high resolution rapid processing techniques are extremely flexible, not needing either masks or resists. Specifically, they have a unique capability to fabricate complex three-dimensional nanostructures on any surface. The main drawback usually found when using these processes is that due to the poor decomposition efficiency of the molecules under focussed beams, the material deposited is a mixture of elements coming from the precursor gas molecules, having properties far from those pursued. Magnetic materials are however the exception to this negative scenario, since under the appropriate growth conditions and using carbonyls of 3d-ferromagnetic metals, pure magnetic materials can be directly deposited. Due to the recent birth of these techniques, previous results using FEBID/FIBID of magnetic materials have been mostly devoted to study the purity of the deposits and to reproduce results previously obtained by standard patterning techniques. This project will go several steps further exploiting the unique capabilities of FE/IBID for the fabrication of magnetic nanostructures. By varying the deposition conditions, a new set of nanomagnetic materials will be studied, where the microstructure and composition will be controlled at the nanoscale. By combining gas precursors and focussed beams, different types of magnetic compounds will be fabricated, as well as multi-layered nanostructures. Moreover, the growth of complex three-dimensional nanomagnets will permit to create the first devices which can store and process magnetic information in all three directions. In order to characterise these systems, a combination of magnetic, structural and spectroscopy techniques together with magnetic imaging and simulations will be used.