SINGLE-CRYSTAL MOSSBAUER AND NEUTRON POWDER DIFFRACTION MEASUREMENTS ON THE SYNTHETIC CLINOPYROXENE LI-ACMITE LIFESI2O6

Mossbauer experiments on a Li-acmite single crystal section with the c rystallographic b-axis (P2(1)/c) parallel to the k-vector of incident gamma-rays were performed at room temperature and at several temperatu res around the previously reported Neel point (19.5(5)K). The observed iron is found to be exclusively in the trivalent state on one crystal lographic site. In the antiferromagnetic region below T-N we observe s trong relaxation effects which diminish with decreasing temperature. I n spite of this, the Mossbauer spectra could be satisfactorily refined yielding a slightly temperature-dependent angle of similar to 42 degr ees between the main component of the electric field gradient efg, V-z z; and b. In contradiction to early Mossbauer powder experiments, the quadrupole splitting QS does not disappear below T-N - a recalculation of the latter spectra with our single crystal parameters (QS not equa l 0, Theta not equal 0) yields at least equal goodness-of-fit as the e arly results. The internal magnetic field H(0) is mainly aligned paral lel to the c-axis in agreement with previous susceptibility measuremen ts. A slight canting towards a corresponds with the results of neutron powder diffraction measurements at low temperatures.