Unique surface sensitivity to ferro- and antiferromagnetic phases by polarization analysis in synchrotron Mossbauer reflectivity

Polarization analysis of the reflected radiation has been performed in Mossbauer reflectivity measurements with a Synchrotron Mossbauer Source (SMS). Effective pi ->sigma' polarization selection is attained with LiF crystal ((6 2 2) 90 degrees-reflection for 14.4 keV radiation, angular acceptance similar to 100 '') capable of high pi ->pi' suppression. Basic features of the reflectivity with the rotated pi ->sigma' polarization are revealed in the experiment with the [Fe-57(10 ML)/V(20 ML)](20) multilayer. Selection of pi ->sigma' polarization component in Mossbauer reflectivity allows to exclude nonresonant electronic scattering, besides Mossbauer pi ->sigma' reflectivity spectra (R-spectra) contain only contributions from magnetized along the beam ferromagnetic phases. The antiferromagnetic iron oxides do not contribute to pi ->sigma' R-spectra (dichroic component is compensated). Therefore, in the Mossbauer reflectivity experiment supplemented by polarization analysis the data interpretation becomes more certain and gives information about depth position for ferromagnetic layers selectively. With this new technique we locate antiferromagnetic iron phases in the very top layer of [Fe-57(10 ML)/V(20 ML)](20) multilayer and ascertain the ferromagnetic ordered iron layers in the remaining part of the structure. This new approach in Mossbauer reflectivity has interesting perspectives for investigations of hyperfine interactions for iron complexes on the surface, ultrathin layers and multilayers with complicated magnetic structures.