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

Abstract

Polarization analysis of the reflected radiation has been performed in Mössbauer reflectivity measurements with a Synchrotron Mössbauer Source (SMS). Effective π→σ′ polarization selection is attained with LiF crystal ((6 2 2) 90o-reflection for 14.4 keV radiation, angular acceptance ∼ 100``) capable of high π→π′ suppression. Basic features of the reflectivity with the rotated π→σ′ polarization are revealed in the experiment with the [57Fe(10 ML)/V(20 ML)]20 multilayer. Selection of π→σ′ polarization component in Mössbauer reflectivity allows to exclude nonresonant electronic scattering, besides Mössbauer π→σ′ reflectivity spectra (R-spectra) contain only contributions from magnetized along the beam ferromagnetic phases. The antiferromagnetic iron oxides do not contribute to π→σ′ R-spectra (dichroic component is compensated). Therefore, in the Mössbauer 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 [57Fe(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 Mössbauer reflectivity has interesting perspectives for investigations of hyperfine interactions for iron complexes on the surface, ultrathin layers and multilayers with complicated magnetic structures.