Neutron polarization analysis studies of both nuclear and magnetic correlations in disordered alloys and compounds provide a unique insight into the character and extent of magnetic disorder in these systems and its dependence on local atomic environment. We present here a review of polarization analysis studies of magnetic and structural defects in a variety of materials, performed using the diffuse scattering spectrometer D7 at the Institut Laue–Langevin. The diverse range of magnetic materials studied using D7 include spin-glasses, frustrated itinerant electron systems, pyrochlores, and quasicrystals.
Dynamic polarization of fluorine nuclei has been examined with 14 free radicals dissolved in hexafluorobenzene (C6F6) and 1,1,1-trifluoro-2,2,2-trichloroethane (CF3CCl3). The radicals may be broadly grouped by their tendency to produce either positive or negative fluorine NMR enhancement. A large positive enhancement indicates that Fermi-contact coupling between the nucleus and the radical electron is the dominant nuclear relaxation mechanism; a large negative enhancement indicates that dipolar coupling is dominant. The correlation times for dipolar and contact relaxation components are comparable, and approximately the values expected from molecular diffusion. The intermolecular contact coupling may be transmitted by exchange polarization of bonding electrons on the fluorocarbon, or by charge transfer between radical and fluorocarbon, or by a combination of both mechanisms. Steric shielding appears to weaken the contact interaction in certain cases; but it is not the sole physical influence governing the contact coupling, nor even necessarily the most important one. The highest fluorine NMR enhancements observed at 74 G were −220 for CF3CCl3 with 2,4,6-tritertiary butyl phenoxyl, and +260 for C6F6 with 2,4,6-triphenyl pyrylyl in acetone.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.