Reduced A-site moment in Fe3O4

Polarised neutron measurements on Fe3O4 had been reported earlier. Fresh data (lambda = 0.91 angstrom) has been collected on 49 reflections in the [110] zone upto sinTHETA/lambda = 0.8263 angstromsup(-1) on a relatively thinner crystal. The problem of extinction has been investigated through the dependence of polarisation ratios on the path lengths in the crystal as well as from supplementary unpolarised neutron measurements (lambda =1.42 angstrom). Double Bragg scattering has been investigated for some reflections by turning the crystal apound the scattering vector. The observed polarisation ratios cannot be explained satisfactorily on the basis of magnetic moments localized only the A and B sites and by incorporating crystal field modifications only of the magnetic electron wave functions. It is concluded that there are significant covalency effects present. An analysis of the A-site-only reflections shows that the A-site moment is significantly reduced (about 3.7 μg) at room temperature compared to its free ion value. The magnetic moment density maps prepared from the zonal data give evidence for density transferred to regions outside the Cation sites and also show that the moment density deviates from spherical symmetry on both A and B-sites. (author)