POLARIZED NEUTRON REFLECTOMETRY WITH POLARIZATION ANALYSIS: AN ULTRA SENSITIVE TOOL FOR THE MAGNETISM OF THIN FILMS. C. Fermon, DRECAM/SPEC, C.E.A Saclay, 91191 Gif/sur/Yvette cedex FRANCE

The polarization analysis gives a vectorial measure of the magnetization in the plane of a thin film. From reflectivity profiles obtained for each state of the incident and reflected neutron spin, it is possible to rebuilt the vectorial magnetic depth profile of multilayers and thin films. The quality of information obtained in thin films is in fact much better than multilayers because there is no averaging and no decrease of the signal. The sensitivity is very high: we can measure the magnetization of a single monolayer with less than 0.05mB per atom. For theoretical simulations we take into account different effects: external magnetic field, neutron precession usually neglected but important in the case of non colinear moments in the layers [1]. I shall describe a new reflectometer with spin analysis PADA built on the Orphée reactor LLB, France. I shall present several examples which show clearly the sensitivity of the method. Spatial correlations and non specular relflectivity will be also discussed.