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Title: R. Kužel, L. Horák: XRD study of strongly oriented thin films, application to hexagonal ferrites with potential magnetoelectric effect
Number: 17/21
Status: Closing date exceeded
Begin: Thursday, 18.03. 2021, 14:00
Tutor: Václav Holý, Milan Dopita
Location: Zoom Meeting ID: 912 8249 6771

nanocent


Nano Seminar

 

Thursday, 18. 3. 2021, 14.00,

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https://cesnet.zoom.us/j/91282496771

Meeting ID: 912 8249 6771

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Radomír Kužel, Lukáš Horák

Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Czech republic

XRD study of strongly oriented thin films, application to hexagonal ferrites with potential magnetoelectric effect

 

X-ray diffraction and reflectivity techniques for analysis of thin polycrystalline thin films have been well-developed and they are routinely used when often low-angle incidence setup is applied instead or in addition to symmetrical q-q scan. However, for strongly oriented films more different asymmetric scans and/or reciprocal space mapping are required. During the study of nanocrystalline ZnO films [1] we have applied a combination of different scans to characterize both the so-called out-of-plane orientation and in-plane orientation. Strong out-of- plane orientations were found, and only basal (00l) reflections were available in symmetric scans. Therefore, the lattice parameters, profile analysis (crystallite size and strains) and residual stresses were studied by combination of several asymmetric reflections scanned at specific suitable angles of inclinations j and y (i.e. on the axis perpendicular to the film surface and axis perpendicular to the goniometer axis, respectively). For comparison of measured lattice parameters there was often a problem of either no data in the PDF-4+ database for specific phase or multiple but different data.

The methods were also used in later extensive study of M, Y, Z and W hexagonal ferrites with a potential of magnetoelectric effect. The films were prepared by chemical solution deposition (CSD) method and metalorganic precursor solutions prepared using the modified Pechini method. Number of processing parameters were tested and optimized with the aim to minimize the impurities that could spoil the magnetic properties of final material. For preparation of highly oriented ferrite films, several substrates were used, and different substrate/seeding layer/ferrite layer architectures were proposed. From seven M phases with different chemical composition, magnetic character and lattice misfit values investigated in their use as template and buffer layers for Y ferrite growth, the best results were achieved when the misfit values between seed layer and substrate, and between seed layer and top Y-layer are approximately equal [2, 3]. 

New Y-ferrite phases were prepared with the composition BaSrZnCoFe11(Me)O22 (Me = Al, Ga, In, Sc). and it was found that for Me = Al, Ga the magnetic structure is of non-colinear ferrimagnetic type with unspecified helical magnetic structure. For Me = Ga this is a new system with potential ME effect. Moreover, these films could be prepared as well-oriented both out-of-plane and in-plane on STO - SrTiO3(111) substrates directly without any seeding layers. ME Z-type ferrite Sr3Co2Fe24O41 and BaxSr3-xCo2Fe24O41 thin films were prepared and characterized for the first time [4]. However, in these films the analysis was complicated by the presence of M and S (spinel) phases that were also oriented (aligned with the substrate) and therefore also many asymmetric reflections were overlapped and many of them were weak. Therefore, a careful selection of reflections suitable for the analysis had to be made. Composition series of W-type SrCo2-xZnxFe16O27 hexaferrite thin films and powders were also successfully synthetized by CSD method.

The XRD analysis of these materials is complicated by the fact that the low-symmetry unit cell of such materials is rather large. Consequently, the number of observable peaks is quite high and their diffraction angles are partially overlapping that makes measurement of pole figures mor ecomplicated. Fortunately, fast 2D detectors are available nowadays also in standard laboratory diffractometers that makes it possible to measure reciprocal-space maps very quickly. In this presentation, the measurements with 2D detector placed closely behind the sample are presented. Using the shorter sample-detector distance, the resolution is partially sacrificed while the reciprocal space area observed by the detector is dramatically extended. In this configuration, the continuous theta-2theta scan fully probes a long stripe in a reciprocal space. By measuring several such stripes, it is easy to reveal the full planar cut of the reciprocal space, and surprisingly the total acquisition time can be only tens of minutes for strongly oriented layers. Moreover, such measurement can be performed for different sample azimuth in order to obtain different planar cuts. This is desirable for single-crystal substrates, for which the surface symmetry can be followed.

The obvious advantage of this approach is a possibility to quickly visualise the intensity in reciprocal space and to compare the obtained images with the simulations based on some expected phase/texture model giving semi-quantitative results. Therefore, it is very suitable for the first-try characterization of the unknown samples.

 

The work was supported by the project NanoCent financed by European Regional Development Fund (ERDF, project No. CZ.02.1.01/0.0/0.0/15.003/0000485)

References:

[1] Z. Matěj, R. Kužel, L. Nichtová. Metallurgical and Materials Transactions A42 (2011) 3323-3332. [2] J. Buršík, R. Uhrecký, D. Kaščáková, M. Slušná, M. Dopita, R. Kužel, Journal of the European Ceramic Society, 26 (2016) 3173-3183.
[3] R. Uhrecký, J. Buršík, M. Soroka, R. Kužel, J. Prokleška, Thin Solid Films, 622 (2017) 104-110. [4] J. Buršík, R. Uhrecký, M. Soroka, R. Kužel, J. Prokleška, Journal of Magnetism and Magnetic Materials, 469 (2019) 245-252.

 

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