Time-resolved nuclear spin-dependent small-angle neutron scattering from polarised proton domains in deuterated solutions

Abstract.: We have investigated the process of dynamic proton polarisation by means of time-resolved polarised small-angle neutron scattering (SANS) on frozen solutions of EHBA-CrV molecules in glycerol-water mixtures as a function of the concentration of EHBA-CrV and for different degrees of deuteration of the solvent. In the EHBA-CrV complex, the spins of the 20 protons which surround the paramagnetic CrV can be oriented using the method of dynamic nuclear polarisation (DNP), thereby offering the possibility to create locally a nuclear spin-dependent contrast for SANS. The time constants which describe the build-up of polarisation around the paramagnetic centre and the subsequent diffusion of polarisation in the solvent were determined by analysing the temporal evolution of the nuclear polarisation, which in turn was obtained by fitting a core-shell model to the time-dependent SANS curves. The results on the spin dynamics obtained using the scattering function of a core-shell could be independently confirmed by evaluating the integrated SANS intensity. A thermodynamic one-centre model is presented which is able to reproduce the observed dependence of the proton polarisation times on the proton concentration of the solven

Magnetic coherence above the Curie point in ferromagnetic LaSrMnO manganites

Small-Angle polarised Neutron Scattering (SANS) measurements have been carried out on a ferromagnetic $\rm La_{0.75}Sr_{0.25}MnO_3$ single crystal. In the vicinity of the Curie point a substantial neutron intensity above $q=0.05\;{\rm \AA}^{-1}$ appears which indicates the presence of nanometre size inhomogeneities mainly of magnetic origin. The neutron spectra cannot be explained with a picture of spin clusters moving in a paramagnetic background, i.e. magnetic polarons. Rather, a model describing an average magnetic coherence extending over several Mn spins leads to very good fits to the data. This situation is comparable to that encountered in Fe or Ni close to Tc but not completely similar. Indeed, magnetic coherence above $T_{\rm c}$ is significantly stronger in the manganites where an unusual spin correlation function had to be used to fit the data

Spin-dependent scattering lengths of slow neutrons with nuclei by pseudomagnetic measurements

The spin-dependent scattering length of slow neutrons by the nuclei 23Na, 59Co, 63Cu, 65Cu, 195Pt, 197Au and 207Pb, as well as the mean value for the two isotopes of Tl and Ag in the natural element have been obtained by measuring the precession of the neutron spins as a function of nuclear polarization. A revised value for 91Zr is also given. The method has been extended for use with magnetic materials. Using f.c.c. and hexagonal cobalt, it is shown that these pseudomagnetic measurements may give precise information on the internal field seen by the nuclei.En mesurant la précession de spin de neutrons en fonction de la polarisation nucléaire, on a obtenu les valeurs de la longueur de diffusion dépendant du spin nucléaire pour les noyaux de 23Na, 59Co, 63Cu, 65Cu, 195Pt, 197Au et 207 Pb, ainsi qu'une valeur moyenne pour les deux isotopes du thallium et de l'argent dans l'élément naturel. On donne également une valeur corrigée pour 91Zr. La méthode a été étendue aux matériaux magnétiques. En utilisant du cobalt c.f.c. et hexagonal, on montre que les mesures pseudomagnétiques peuvent fournir des informations précises sur le champ interne vu par les noyaux

Experimental values of spin dependent nuclear scattering lengths of slow neutrons

The principle of the method of pseudomagnetism for measuring spin dépendent scattering lengths of slow neutrons on nuclei is recalled. A table is given which reviews the results obtained with this method. It contains previously published values, some of them corrected following careful remeasurement, as well as other hitherto unpublished values.Après avoir rappelé le principe de la mesure par la méthode du pseudomagnétisme, des longueurs de diffusion neutroniques dépendant du spin des noyaux on donne un tableau qui rassemble les résultats obtenus par cette méthode. Il contient des valeurs déjà publiées. Mais certaines ont cependant subi des corrections à la suite de nouvelles mesures plus précises. Le tableau contient en outre des résultats nouveaux

Small-angle scattering of polarized neutrons in HTSC ceramics

URL: http://www-spht.cea.fr/articles/S97/169 First European Conference on Neutron Scattering, Interlaken, Switzerland, October 8-11, 1996; Org.: Bauer G.S., Boniand P., Fischer P.The results of the first observation of the small-angle polarized neutron scattering (SAPNS) from magnetic flux inhomogeneities in high-$T_c$ Y-Ba-Cu-O and La-Sr-Cu-O ceramics are reported. The difference between the scattering cross sections for neutrons initially polarized along or opposite to the applied field was found at $