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Using spectroscopic ellipsometry and Raman spectroscopy, we measured the pseudodielectric function and the phonon frequencies of fluorinated nanocrystalline carbon (nc-C:F) thin films grown on silicon substrate at varying growth temperature and gas flux ratio of CH[sub 4] and CF[sub 4]. Utilizing the Tauc–Lorentzian formula, we performed multilayer analysis to estimate the dielectric function of the fluorinated nanocrystalline carbon thin films. We also adopted Gaussian-like density-of-states model proposed by Demichelis et al. [Phys. Rev. B 45, 14364 (1992)] and estimated the amplitude A, the transition energy E[sub π], and the broadening σ[sub π] of π→π[sup *] transitions. Based on this model, we explained the change of the optical gap and the refractive index in terms of the change of the amplitude A rather than the shift of transition energy E[sub π] of π→π[sup *] transitions. Raman and ellipsometric study suggested that the average size of nanocrystallites in the fluorinated carbon thin films was smaller than that of amorphous hydrogenated carbon films studied by Hong et al. [Thin Solid Films 352, 41 (1999)]. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Phonon softening in hexagonal BaFe12O19 single crystal is observed in temperature dependent polarized Raman spectroscopy. The phonon softening is significantly enhanced below ∼80 K, at which the magnetization in a magnetic field along c-axis shows a clear change in the temperature dependence, indicating a magnetic phase transition near 80 K. Possible interpretations of the anomalous temperature dependence of the phonon frequencies-phonon softening behaviors are discussed. The phonon softening would be correlated to local structural and magnetic phase transition in hexagonal BaFe12O19, in which the spin-phonon coupling would have major contribution for the phonon softening. We also discuss that the spin-phonon coupling would be affected by both the spin ordering and the individual phonon vibration in magnetic material. [ABSTRACT FROM AUTHOR]

We present the results of an optical method of quantitatively estimating the spin exchange interactions in hexagonal manganites RMnO3 (R = Tb, Dy, Ho, Er) epitaxial thin films. The two in-plane (a-b plane) spin exchange integrals J1 (intratrimer Mn-Mn interaction) and J2 (intertrimer Mn-Mn interaction) are deduced from the magnon scattering peak wavenumbers. We found that J2 decreases systematically when the R ionic radius increases, while J1 is nearly independent of R ionic radius, contrary to the expectation in single crystals. We show that the R dependence of J1 could be understood in terms of the stress in the thin films. Our result indicates that the stress has stronger effect on the atomic displacement of the intratrimer Mn-Mn distance than the intertrimer Mn-Mn distance. [ABSTRACT FROM AUTHOR]

A correction to the article "Spin exchange interactions in hexagonal manganites RMNO (R=Tb, Dy, Ho, Er) epitaxial thin films," that was published in the 2011 issue is presented.