The structure of the thermotropic cubic phases of 4 ¾ -n -alkoxy-3 ¾ -nitrobiphenyl-4-carboxylic acids (ANBC-n , where n indicates the number of carbon atoms in the alkoxy group) was studied by X-ray di V raction. For the homologues with n= 15, 16, 17, and 18, the cubic phase was of an Ia 3 d type, whereas the homologues with n = 19, 20, and 21 exhibited an Im 3 m cubic structure; for these seven homologues the same type of cubic structure was observed both on heating and cooling. Further lengthening of the alkoxy chain to n= 22 and 26, however, gave two types of cubic structure in the cubic phase region on heating, one with Im 3 m symmetry in the low temperature region and the other with Ia 3 d symmetry in the high temperature region. On cooling, the two homologues exhibited the Ia 3 d cubic structure only. This is the rst example in the cubic phase region of a series of homologues containing two types of structure, dependent on temperature and n . Such a complicated phase diagram in the cubic region is clearly understood qualitatively in terms of Gibbs free energy-temperature diagrams. The dependence of structural parameters such as the cubic lattice constant on the alkoxy chain length n are also presented and discussed.
La0.7Sr0.3MnO3 (LSMO) thin films grown by pulsed laser deposition on SrTiO3 (STO) substrates with (1 0 0) and (1 1 0) crystallographic orientations are characterized by means of magneto-optic (MO) ‘Kerr’ spectroscopy at polar and longitudinal magnetizations combined with spectroscopic ellipsometry (SE) in the photon energy range between 1.2 and 4.8 eV. The LSMO film thickness, t, ranges from 10 to 50 nm. Amplitudes in the permittivity tensor spectra, determined from the MO and SE data, depend on t and substrate orientation. The magnetization onset is faster in the films grown on (1 1 0) substrates, probably due to lower strain induced by (1 1 0) substrates. In the films grown on (1 0 0) substrates, the polar and longitudinal MO ‘Kerr’ spectra can be reasonably explained assuming the diagonal elements of the permittivity tensor to be equal to each other and the off-diagonal elements deduced from the MO polar ‘Kerr’ spectroscopy. This approach applied to the films grown on (1 1 0) substrates also provides the expected spectral shape; the computed amplitudes are stronger than the observed ones which suggests that the surface morphology affects the permittivity tensor elements in some way. The agreement of the permittivity tensor spectra with those acquired on sintered samples and thick films confirms a perfectly developed perovskite structure even at 10 nm. The study shows that MO spectroscopy and SE can be used for a fast, cheap and efficient diagnostics of the LSMO films in the thickness range relevant for device applications. A low noise level in MO polar ‘Kerr’ spectra on the thinnest samples (t ≈ 10 nm) indicates that the presence of the room temperature magnetization and LSMO characteristics in MO spectra can safely be detected in films of t ≈ 5 nm.
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