MAGNETIC DEFECTS OBSERVED BY SMALL-ANGLE NEUTRON-SCATTERING IN APPLIED MAGNETIC-FIELDS IN A WEAKLY FRUSTRATED SYSTEM

Small angle neutron diffraction measurements have been performed on a 'reentrant' polycrystalline Ni//1// minus //xMn//x alloy as a function of temperature and applied magnetic field. In applied fields, the scattering I(q) exhibits a peak which moves towards higher value as the field increases, while the total intensity strongly decreases. All these variations take place at nearly constant magnetization. The magnetic scattering I(q) obtained for different field values is shown to obey an approximate scaling law. These results can be interpreted in terms of the existence of rather well defined clusters (magnetic defects). Within this model, these experiments provide the observation of the variation of their size and density with field and temperature. Finally, very similar observations have been made for amorphous (FeMn)//7//5P//1//6B//6Al//3.