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

点击翻译按钮获取中文摘要

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.