Ramanspektroskopische Untersuchungen an multiferroischen epitaktischen Dünnschichten
Zusammenfassung der Projektergebnisse
The main results achieved are summarized in the following: Temperature-dependent Raman spectroscopy and X-ray diffraction measurements were employed to study the structural phase transition between monoclinic and orthorhombic phases in polycristalline BiCrO3 and to determine the transition temperature. - The dielectric function and band gap of BiCrO3 films was determined for the first time based on spectroscopic ellipsometry results. - The epitaxial relation between BiCrO3 films and different substrates (NdGaO3, LSAT) was determined by using azimuthal / polarisation-dependent Raman measurements corroborated with simulations based on crystal symmetry and with X-ray diffraction results. A similar method was employed for the characterisation of the feroelectric / feroelastic domain structure in the case of epitaxial BiFeO3 films deposited on rare earth scandate substrates. - Raman studies have confirmed very good epitaxy of the tetragonal-like (T-like) BiFeO3 films grown on LaAlO3 substrates, as indicated by the remarkable azimuthal / polarisation dependence of the Raman spectra. The larger numbers of phonons observed in the spectra of T-like BFO films as compared with that of R-like BFO films is consistent with a Cc monoclinic structure, with a large tetragonal c/a ratio. The dielectric function and the bandgap of T-like BFO are blue shifted by ca. 0.3 eV as compared with the not strained films (R-like). - Grüneisen parameters for BiFeO3 epitaxial thin films have been determined from the relative volume change and the relative shifts of the Raman modes induced by the piezoelectric strain. - The crystalline structure in NiFe2O4 and CoFe2O4 thin films and sub-micron structures was investigated by Raman spectroscopy and thereby a strain induced symmetry lowering was evidenced. - The band gap as well as the diagonal and the off-diagonal components of the dielectric function of ferrimagnetic NiFe2O4 and CoFe2O4 epitaxial thin films grown on Nb-doped SrTiO3 substrates were determined in the spectral range from 0.7 eV (diagonal) and from 1.7 eV (off-diagonal) to 5 eV by combining spectroscopic ellipsometry and magneto-optical Kerr effect measurements.
Projektbezogene Publikationen (Auswahl)
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Raman spectra and dielectric function of BiCrO3: Experimental and first-principles studies. J. Appl. Phys. 110 (2011), 073501_1-8
C. Himcinschi, I. Vrejoiu, T. Weißbach, K. Vijayanandhini, A. Talkenberger, C. Röder, S. Bahmann, D. R. T. Zahn, A. A. Belik, D. Rafaja, and J. Kortus
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Raman spectroscopic and X-ray diffraction investigations of epitaxial BiCrO3 thin films. Thin Solid Films 520 (2012), 4590–4594
A. Talkenberger, C. Himcinschi, T. Weißbach, K. Vijayanandhini, I. Vrejoiu, C. Röder, D. Rafaja, and J. Kortus
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Migration-induced field-stabilized polar phase in strontium titanate single crystals at room temperature. Phys. Rev. B 88 (2013) 024104_1-10
J. Hanzig, M. Zschornak, F. Hanzig, E. Mehner, H. Stöcker, B. Abendroth, C. Röder, A. Talkenberger, G. Schreiber, D. Rafaja, S. Gemming, and D.C. Meyer
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Optical and magneto-optical study of nickel and cobalt ferrite epitaxial thin films and submicron structures. J. Appl. Phys. 113 (2013), 084101_1-8
C. Himcinschi, I. Vrejoiu, G. Salvan, M. Fronk, A. Talkenberger, D.R.T. Zahn, D. Rafaja, and J. Kortus
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Magnetic field dependent thermal conductance in La0.67Ca0.33MnO3. Journal of Magnetism and Magnetic Materials 381 (2015) 188
C. Euler, P. Hołuj, A. Talkenberger, G. Jakob
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Optical properties of epitaxial BiFeO3 thin films grown on LaAlO3. Appl. Phys. Lett. 106 (2015) 012908_1-5
C. Himcinschi, A. Bhatnagar, A. Talkenberger, M. Barchuk, D.R.T. Zahn, D. Rafaja, J. Kortus, and M. Alexe
