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Ultrasmooth magnetic layers for advanced devices

Final Activity Report Summary - ULTRASMOOTH (Ultrasmooth magnetic layers for advanced devices)

Ultrasmooth was a research training network (RTN) funded under the Marie Curie initiative. As an RTN, the emphasis on activity in Ultrasmooth was on the provision of training and experience beyond that obtainable in a single laboratory. The rationale guiding the training was the production of improved metallic layers by the novel use of particle beams to smooth either substrates before deposition or influence the properties of layers after deposition. Alternatively, growth techniques were used in several centres to also explore possibilities of producing better quality layers. Samples produced in this way were characterised by transport, neutron and x-ray scattering. The connection to real devices was made through the inclusion of several industrial partners.

The consortium set out to deliver 324 person-months of training and this was exactly achieved. We trained 12 researchers in state-of-the-art layer production, irradiation and characterisation techniques and all researchers worked in another relevant area in addition. This training was achieved through host provision as well as exchanges and secondments. Researchers undertook organisation of network meetings, responsibility for content of presentations at specific meetings and generic training formed part of summer school programme which gave them the necessary experience to take on the job of forming the core organisation team of the KT workshop held in the final year. Some researchers won time at international research facilities. Over 30 joint publications between partners, 11 conference presentations of joint work, and 24 conference talks by researchers were made at international meetings. Two ESRs have obtained their PhDs and taken up postdoctoral positions and most ERs have obtained permanent positions that are scientific in nature.

Selected scientific highlights include the production of world-class tunnel junctions using MgO barriers, the growth of new epitaxial Heusler alloys, the exploitation of the nanostencil technique for the production of magnetic nanostructures and the study of roughness and magnetic anisotropies have been achieved. Samples produced by the partner labs involved pre- and post-irradiation where clear, unambiguous demonstrations of the smoothing effects on transition metal systems and MgO substrates has been achieved with a high degree of physical understanding. In addition, the transport properties of CoFeB/MgO/CoFeB magnetic tunnel junctions has been greatly improved by irradiation and the interface demixing and smoothing effects of using 30 keV Helium ions in immiscible multilayer systems have been studied. Using advanced characterisation tools it has been found that using MgO as the spacer in Heusler multilayers, much smoother interfaces can be realised than in the case of AlOx spacer layers. This has important consequences for the future design of tunnelling barriers in TMR devices. By analysing CoFeB/MgO multilayers by hard x-ray reflectivity, new understanding on the interplay between diffuse and specular scattering has been discovered. It turns out that depending on the slit size of the detector, diffuse scattering is detected simultaneously with specularly reflected intensity. We could show that by taking into account the instrumental resolution of the set-up used, the reflectivity can only be explained by a combination of the diffuse part of the scattering and not only the specular, as previously assumed. Results aimed at devices have concentrated on magnetic tunnel junctions and their applications and include the fabrication by sputtering of tunnel junctions for MRAM applications with TMR of app. 240%, lower resistance tunnel junctions for current switching applications and the achievement of a better linear response using thinner CoFeB free layers and their application as sensors for biochips.