D3 - The Spin Polarised Hot Neutron Beam Facility

Determination of the magnetization distribution in Cr2O3 using spherical neutron polarimetry

The magnetization distribution in the antiferromagnet Cr2O3 (where the nuclear and magnetic scattering appear in the same reflections and are in phase quadrature) has been determined with good precision using spherical neutron polarimetry.

The determined total moment associated with each Cr3+ ion is only 2.48 μB rather than the predicted 2.97 μB. The loss of moment can be attributed to covalent mixing of the Cr 3d electrons with O 2p orbitals in π-type antibonding orbitals.

Positive and negative spin transferred to O from oppositely polarized Cr3+ ions is superposed and so does not contribute to the magnetization. There are some significant features in the magnetization distribution (see fig.) which are not accounted for by the ionic model. They occur in regions where the Cr and O radial wavefunctions overlap strongly and are hence probably due to covalent overlap.

Ref.: P. J. Brown, J. B. Forsyth, E. Lelièvre-Berna and F. Tasset
, J. Phys.: Condens. Matter 14 (2002) 1957–1966.