Spherical neutron polarimetry (SNP), as implemented at ILL with the second-generation zero-field polarimeter CRYOPAD II, enables to orient precisely the spin polarisation vector in the incident thermal neutron beam and to measure how it is changed (amplitude and direction) by interaction with the sample. For neutrons scattered by excitations in low-dimension magnetic systems, the components which are transverse to the initial polarisation direction are large and could be recently and systematically observed by Regnault ct al. (Physica B 267-258 (1999) 227.). Maleyev has shown that such transverse components can arise uniquely from the existence of mixed nuclear-magnetic Van-Hove pair correlation Functions. Therefore, neutron scattering is telling us that the excitations are strongly hybridized. We discuss a hat al e the most important technical features of this ultimate polarised neutron technique in view of this fascinating application of inelastic neutron scattering for the years to come. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 15]
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