NEUTRON STUDY OF THE SPINEL COMPOUNDS FE2-2TMG1-THRESHOLD OF THE DOMINANT INTERACTION(TTITO4 ACROSS THE PERCOLATION)

We have performed neutron diffraction, neutron diffuse scattering and quasielastic neutron scattering in the ferrimagnetic frustrated insula ting compounds Fe2-2tMg1+tTitO4. We have studied the concentration, te mperature, and field dependence of the spin correlations, in a concent ration range (0.5 less than or equal to t less than or equal to 0.7) e ncompassing the percolation threshold (t(I) = 0.68) of the dominant in teraction. For t < t(I), we observe a magnetic contribution to the Bra gg peaks. It coexists with a diffuse quasielastic scattering, which pe rsists in a wide concentration and temperature range. Typical effects of magnetic frustration are observed at low temperature. In particular , the concentration dependence of the short-range correlation length d oes not obey the behavior expected from a chemical percolation approac h.