STUDYING LONG-RANGE SPIN ORDERING ON SURFACES BY METASTABLE HE-2(3)S SCATTERING

We have developed a technique for using diffractive scattering of meta stable 2(3)S He (He) to determine the long-range electron spin orderi ng on the surfaces of magnetic insulators. The technique is based on t he fact that the probability of He surviving a scattering event can b e significantly enhanced when an appropriately located electron energy gap and localized spins are present on the surface. A periodic arrang ement of the orientation of the local moments on the surface then lead s to a periodic modulation of the beam attenuation that is reflected i n the corresponding diffraction pattern. In these initial studies, we measured the electron spin-ordering on a NiO (100) surface, and found a structure of periodicity (6 x 1), which is quite different from the bulk antiferromagnetic arrangement. We modeled the scattering process using a modified version of the eikonal approximation, in which a diss ipative hard corrugated wall simulates the spatially modulated attenua tion of the He beam. Calculations performed on this model were in good qualitative agreement with our experimental data.