NATURAL LINEAR DICHROISM AT THE FE 2P ABSORPTION-EDGE OF GILLESPITE

We observed a strong polarization dependence in the double peak struct ures at Fe2p absorption edges of BaFeSi4O10, which agrees with atomic multiplet calculations for a d(6) (5)A(1) ground state in square plana r symmetry. The quadrupole moment is obtained from the sum rule for th e integrated intensity of the linear dichroism. The analysis of the br anching ratio and the details of the spectral shape give evidence conf irming that the pressure induced structural phase transition in gilles pite has a crystal field origin rather than being due to a high to low spin transition.