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Under the terms of the Creative Commons Attribution 3.0 Unported License to their work. ; The morphology and the quantitative composition of the Fe-Si interface layer forming at each Fe layer of a (Fe/Si)3 multilayer have been determined by means of conversion electron Mössbauer spectroscopy (CEMS) and high-resolution transmission electron microscopy (HRTEM). For the CEMS measurements, each layer was selected by depositing the Mössbauer active 57Fe isotope with 95% enrichment. Samples with Fe layers of nominal thickness dFe = 2.6 nm and Si spacers of dSi = 1.5 nm were prepared by thermal evaporation onto a GaAs(001) substrate with an intermediate Ag(001) buffer layer. HRTEM images showed that Si layers grow amorphous and the epitaxial growth of the Fe is good only for the first deposited layer. The CEMS spectra show that at all Fe/Si and Si/Fe interfaces a paramagnetic c-Fe1− x Si phase is formed, which contains 16% of the nominal Fe deposited in the Fe layer. The bottom Fe layer, which is in contact with the Ag buffer, also contains α-Fe and an Fe1− x Si x alloy that cannot be attributed to a single phase. In contrast, the other two layers only comprise an Fe1− x Si x alloy with a Si concentration of ≃0.15, but no α-Fe. ; The financial support of the Spanish MINECO MAT2011- 23791, the Aragonese DGA-IMANA E34 (co-funded by Fondo Social Europeo) and that received from the European Union FEDER funds is acknowledged. L.B.-R. acknowledges the Spanish MINECO FPU 2010 grant. ; Peer Reviewed

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY). ; The intramolecular exchange interactions within the single-molecule magnet (SMM) "butterfly" molecule [Fe3Ln(μ3-O) 2(CCl3COO)8(H2O)(THF)3], where Ln(III) represents a lanthanide cation, are determined in a combined experimental [x-ray magnetic circular dichroism (XMCD) and vibrating sample magnetometer (VSM)] and theoretical work. Compounds with Ln=Gd and Dy, which represent extreme cases where the rare earth presents single-ion isotropic and uniaxial anisotropy, on one hand, and with Ln=Lu and Y(III) as pseudolanthanide substitutions that supply a nonmagnetic Ln reference case, on the other hand, are studied. The Dy single-ion uniaxial anisotropy is estimated from ab initio calculations. Low-temperature (T 2.5 K) hard x-ray XMCD at the Ln L 2,3 edges and VSM measurements as a function of the field indicate that the Ln moment dominates the polarization of the molecule by the applied field. Within the {Fe3LnO2} cluster the Ln-Fe3 subcluster interaction is determined to be antiferromagnetic in both Dy and Gd compounds, with values J Dy-Fe3=-0.4 K and J Gd-Fe3=-0.25 K, by fitting to spin Hamiltonian simulations that consider the competing effects of intracluster interactions and the external applied magnetic field. In the uniaxial anisotropic {Fe3DyO2} case, a field-induced reorientation of the Fe3 and Dy spins from an antiparallel to a parallel orientation takes place at a threshold field (μ0H=4 T). In contrast, in isotropic {Fe3GdO2} this reorientation does not occur. © 2013 American Physical Society. ; The financial support of Spanish MINECO Grant No. MAT2011-23791, the Alexander Von Humboldt Foundation (D.P.), and Aragonese DGA-IMANA E34 (cofunded by Fondo Social Europeo) and that received from European Union FEDER funds are also acknowledged. L.B.R. acknowledges the Spanish MINECO FPU 2010 grant. ; Peer Reviewed