Mossbauer study of Fe-doped CuGeO3 system Cu0.9Ge0.9Fe0.2O3

The Fe-doped system Cu0.9Ge0.9Fe0.2O3 has been investigated by means of X-r ay diffractometry, Mossbauer spectroscopy and superconducting quantum inter ference device. The structure of this system is orthorhombic and the lattic e constants are a = 4.784 Angstrom b = 8.472 Angstrom and c = 2.904 Angstro m, respectively. Magnetic measurements confirm that the spin-Peierls transi tion appears in our sample at about 12 K, which is near to the spin-Peierls transition temperature (T-sp) 14 K of pure CuGeO3 system. The Mossbauer spectrum shows the superposition of two Zeeman sextets and a broad central line due to Fe3+ ions from room temperature to 4.2 K. The Mos sbauer parameters show a discontinuity near T-sp. The jump of the magnetic hyperfine field at temperatures lower than T-sp means increasing of the sup erexchange interaction among the magnetic ions. The jump of the quadrupole splitting and the isomer shift values could be interpreted as due to decrem ent in symmetry of lattice sites and spontaneous thermal contraction.