Spectroscopic ellipsometry study of optical anisotropy in Gd5Si2Ge2 and comparison with reflectance difference spectra

Recently, Gd$_{5}$Si$_{2}$Ge$_{2}$ has been extensively studied due to its giant magneto-caloric effect, colossal magnetostriction, and giant magnetoresistance in the region of an unusual first-order magnetic-structural phase transformation. In this presentation, we report the complex dielectric functions of single crystals of Gd$_{5}$Si$_{2}$Ge$_{2}$ obtained using spectroscopic ellipsometry (SE) in the photon energy range 1.5 to 5.0 eV. Reflectance difference (RD) spectra for Gd$_{5}$Si$_{2}$Ge$_{2}$ single crystals have been measured by reflectance difference spectroscopy (RDS). Reflectance difference spectra for the $a-b$ and $b-c$ planes of single crystals of Gd$_{5}$Si$_{2}$Ge$_{2}$ were derived from the complex dielectric functions obtained from SE measurements and compared with those obtained from RDS measurements at near normal incidence. The measured spectra agreed well. The in-plane optical anisotropy of the sample is mainly due to intrinsic bulk properties because it has large values (4$\times $10$^{-2})$ compared to surface induced optical anisotropies, with values of only of about 10$^{-3}$ for a typical cubic material.