Determination of atomic site susceptibility tensors from polarized neutrondiffraction data

Abstract

Polarized neutron diffraction provides information about themagnetization density of each individual crystallographic site. In thepresent paper the role of the atomic site susceptibility tensor χijaccounting for the magnetic response of individual atoms to an external magneticfield is discussed. The symmetry of this tensor is very similar to that of the tensoruijdescribing the thermal motion of atoms. By analogy with the atomicdisplacement parameters (ADPs), atomic susceptibility parameters (ASPs) can beintroduced. The six independent ASPs can be determined from polarizedneutron flipping ratio measurements and visualized as magnetic ellipsoidswhich are analogous to the thermal ellipsoids obtained from ADPs. If thelocal anisotropy is small, these magnetic ellipsoids approximate to sphereswith diameters proportional to the induced magnetization. In other cases,anomalous (elongated or flattened) ellipsoids will occur. The ASPs have beendetermined for the compound Nd3−xS4 which has the Th3P4 structure.They correspond to strongly oblate magnetic ellipsoids; in contrast, in theisomorphous compound Sm3Te4 the magnetic ellipsoids are found to be prolate.