A Mossbauer study of divalent iron in silver chloride crystals
The temperature dependence. of the quadrupole splitting and the quadrupole relaxation rate has been investigated by means of the Mossbauer effect for divalent iron, initially diffused as S7Co into single crystals of silver chloride. The divalent iron ion substitutes for the monovalent silver ion and associates with a charge compensating positive ion vacancy in a next nearest neighbor site. The distortion of the cubic environment of the iron ion by the vacancy produces the quadrupole splitting. The thermal motion of the vacancy around the iron ion gives rise to random fluctuations in the electric field gradient at the iron nucleus (quadrupole relaxation). Using a suitable model to describe the Mossbauer line shape in the presence of fluctuating hyperfine fields we have measured the activation energy for a vacancy jump and obtained, E = (0.07 ± 0.02)eV. Mossbauer measurements on single crystals of AgCl(Fe++) in magnetic fields at 4.20K showed that the sign of the quadrupole interaction is positive. The interpretation of the magnetic field measurements in the spin Hamiltonian formalism also were consistent with the vacancies occupying next-nearest neighbor sites with respect to the Fe+ + impurity. Methods for the calculation of theoretical Mossbauer spectra in fluctuating and static hyperfine fields are developed and used in the interpretation of the Mossbauer measurements.
Mossbauer, divalent iron, silver chloride crystals, quadrupole relaxation rate, quadrupole splitting
University of Illinois - Urbana-Champaign
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