Optical and magneto-optical tensor spectra of bismuth-substituted yttrium-iron-garnet films

We report on the complete dielectric tensor spectra of Y3−xBixFe5O12 with 0≤x≤1.42 in the photon energy range 1≤ℏω(eV)≤4.8, i.e., 1240–248 nm wavelength. In an attempt to identify the involved optical transitions we have (i) parametrized these spectra in terms of Gaussian (ε″11 spectra) and diamagnetic or paramagnetic (ε′12 and ε″12 spectra) line shapes, and (ii) come up with a set of coefficients of a cubic interpolation polynomial for each spectral ‘‘line’’ from which any of the n, α, ΘF, εF, ΘK, εK, ε′11, ε″11, ε′12, ε″12 spectra can be calculated for any bismuth substitution in the above compositional and spectral range. It is found that such a line-shape analysis is not unique and requires physical knowledge on the optical excitations involved which, however, is still incomplete for iron garnets.