Crystallographic, magnetic and optical properties of I2. Mn.IV.VI4. compounds with I = Cu, log., IV-Si, GE, Sn and VI =S, Se, Te.

Abstract

A systematic study was performed on the structural, magnetic and optical properties of polycrystalline I$\sb2$.Mn.IV.VI$\sb4$ compounds with I = Ag or Cu, IV = Si, Ge, Sn, VI = S, Se and Te. In X-ray diffractometry, three different crystal structures were observed, two corresponding to the tetragonal stannite and orthorhombic wurtz-stannite structures reported previously, and thirdly a cubic rock salt-like structure. Magnetic susceptibility ($\chi$) measurements showed that most of the selenide phases were ferrimagnetic. Optical absorption measurements were made to determine values of optical energy gap E$\sb{\rm o}$ for a number of the single phase samples. When the values of these various parameters ($\rm a\sb{e}, T\sb{N}, \theta\sb{a}$ and E$\sb{\rm o}$) were compared for the various phases, it was found that the phases could be classified into five different sets. In each case investigated, the variation of E$\sb{\rm o}$ with temperature was found to agree well with the theoretical predictions of Alexander et al. (76A1). (Abstract shortened by UMI.)