Experimental attempts to measure non-collinear local magnetisation Original Research Article

Representing atomic magnetic moments as simple vectors has limitations when applied to systems in which orbital moments, or significant spin–orbit coupling is present. These phenomena are associated with interactions leading to non-collinearity in the magnetisation distribution. Several experimental techniques are available to probe such non-collinearity. The most direct is to measure both the magnitude and direction of the magnetic interaction vectors, which give its Fourier components. Such measurements are now becoming possible for antiferromagnets with the advent of a new generation of neutron polarimeters, which will allow both greater geometric flexibility and higher precision. However, up to now non-collinear magnetisation distributions have been revealed by more indirect means. Polarised neutron flipping ratio measurements can give only a single component of the magnetic interaction vector directly. However, the special geometric properties of the interaction vector and the symmetry breaking properties of an applied field can be exploited to obtain evidence of non-collinearity in the magnetisation distribution even from such limited data.