NEUTRON SPECTROSCOPY AND ANISOTROPY OF THE MAGNETIC-PROPERTIES OF UOS- INTERPRETATION IN A CRYSTAL-FIELD AND MOLECULAR-FIELD MODEL

Uranium oxysulphide is an ionic compound whose magnetic and thermodyna mic properties have been extensively studied in the past. UOS becomes antiferromagnetic below T-N = 55 K with an ordered moment mu(ord) simi lar or equal to 2 mu(B). A previous neutron crystal field (CF) spectro scopy experiment was performed to observe the splitting of the J = 4 g round manifold. Two possible CF level schemes were proposed in order t o interpret the results, differing essentially for the presence of the intense Gamma(t5)((1))-->Gamma(t4) transition at low energy (< 10 meV ). One of the aims of this work was to look for a peak in this range o f energy, which was not accessible at the time of the first experiment . Another goal was to test the CF model against a careful study of the anisotropic magnetic susceptibility of high-quality single crystals. The results of these new measurements are presented and discussed in t he frame of a self-consistent molecular field model taking into accoun t the exchange anisotropy.