Electrochemical synthesis and magnetic characterization of Fe1-x-yAlxSiy alloys
Solid State and Surface Chemistry, Material Synthesis
Final Report Abstract
The target of the project was the preparation of magnetic Fe1−x−y Six Aly films in ionic liquids and their magnetic characterization. Firstly Fe, Al, and Si films in ionic liquids were prepared, followed by films FeAl and FeSi made by codeposition, and finally FeSiAl. In all experiments the composition and the morphology of the alloys were varied by the experimental conditions. The magnetic properties of the deposits were measured with an in-house developed magnetic hysteresis measurement system. The whole system was adopted and optimized for measuring the deposited magnetic films. A deposition of magnetic films was done with various ionic liquids, but finally a deposition of a magnetic film from the liquids 1- butyl-1-methylpyrrolidinium trifluoromethylsulfonate, [Py1,4 ]TfO, and 1-butylpyrrolidine together with the salts iron(II) trifluoromethylsulfonate (Fe(TfO)2 ), iron(II) chloride (FeCl2 ), AlCl3 , and SiCl4 achieved the best results. To reduce the high viscosity of some of the mixtures the deposition temperature was around 90◦ C. Magnetic films with a thickness of around 10-15 µm could be prepared and characterized. In cyclic voltamograms the deposition behaviour was investigated and the potentials for co-deposition of alloys were found. By varying the deposition potential the composition of the alloys could be modified in a wide range. The composition of the deposits was controlled by X-ray diffraction and by magnetic saturation polarization. In the alloys FeAl and FeSi the aluminium and silicon content were varied between 0 and 5%, FeSiAl the aluminium content was varied between 0 and 5% and the silicon content between 0 and 4.5%. The grain sizes in the dense deposits were between 30 and 100nm which was determined by XRD broadening, measurement of coercive forces and high resolution SEM. In diffractogramms of the prepared magnetic films often non-magnetic fcc iron was observed. The magnetic properties of the soft magnetic materials are not at par with existing soft magnetic materials due to particle sizes in the nanometer regime. Especially, our work has shown that the classical losses are negligibly small while losses related to domain wall movement are dominant until a polarization of approximately 1.9T is reached. For polarization above 1.9T power losses related to domain wall annihilation and recreation as well as for rotating processes of the magnetic moments into the direction of the external field are the dominant loss mechanisms. An improvement of the magnetic properties can be reached by an orientation of the grains in the easy magnetic axis, by a further reduction of the grain sizes and a reduction of the content of fcc Fe in the electrodeposited layers. The electrodeposited layers have unexpectedly shown random magnetic anisotropy which was likely due to uncontrolled magnetic fields in the glove box due to magnetic stirrers, heaters, transformers for the light sources or simply by electric cables from other running experiments complicating the interpretation of the magnetic results. It was not able to locate the sources for the magnetic anisotropy and in future experiments the deposition experiments must be performed in a box free of static and dynamic magnetic fields, e.g. by using µ-metal. Moreover, it can be assumed that many grains in the electrodeposited samples are misoriented relative to the external field which can be seen in the significant shear of the hysteresis curves measured in our system and in Kerr measurements. Furthermore, internal friction measurements have shown internal stresses and solute iron atoms in copper substrates and vice versa. Internal stresses lead to a dramatic change of the magnetostriction and the magnetic properties of Fe base alloys.
Publications
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Electrodeposition of Al from 1-butylpyrrolidine-AlCl3 ionic liquid, Progress in Natural Science: Materials International 25 (2015) 603-611
G. Pulletikurthi, B. Bödecker, A. Borodin, B. Weidenfeller, F. Endres
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How a Transition Metal(II) Chloride Interacts with an Eutectic AlCl3 -based Ionic Liquid: Insights into the speciation of the Electrolyte and electrodeposition of Magnetic Materials, Chemistry - an Asian Journal 12 (2017) 2684-2693
G. Pulletikurthi, B. Weidenfeller, A. Borodin, J. C. Namyslo, and F. Endres
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Anomalous electroless deposition of less noble metals on Cu in ionic liquids and its application towards battery electrodes, Faraday Discuss. 206 (2018) 339-351
A. Lahiri, N. Borisenko, M. Olschewski, G. Pulletikurthi, F. Endres
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Damping of Fe-Al Alloy Electrodeposited in an Ionic Liquid, Materials Research. 21(suppl. 2) (2018) e20170805
O.A. Lambri, B. Weidenfeller, F.G. Bonifacich, G. Pulletikurthi, J. Xu, L. Weidenfeller, F. Endres
