Fe-porphyrin monolayers on ferromagnetic substrates: Electronic structure and magnetic coupling strength

Abstract

In this work, the different coupling strengths of Fe-octaethylporphyrin molecules sublimated in situ onto epitaxially grown Co and Ni films on Cu(100) are studied by systematic x-ray-absorption and x-ray magnetic circular dichroism (XMCD) measurements. The fine structures observed in the absorption and dichroic spectra of the $\mathrm{Fe}\text{\ensuremath{-}}{L}_{2,3}$ edges are explained in terms of different $\mathrm{Fe}\phantom{\rule{0.2em}{0ex}}3d$ orbitals probed in angular-dependent measurements. The coverage of Fe-porphyrin molecules is varied from submonolayer to 1.5 ML (monolayer), and measurements were carried out at room as well as at low temperatures. From the temperature dependence of the Fe-XMCD signal, a weaker coupling strength between the Fe atom and the Ni substrate is found as compared to the Co case.