Experimental and theoretical investigations of magnetic anisotropy and magnetic hardening at molecule/ferromagnet interfaces

Abstract

We measure by means of in situ magneto-optical Kerr effect the magnetism of ultrathin magnetic films supported on gold and platinum during the capping with molecular layers. We observe both for C60 and Alq3 molecules deposited on Co films an enhancement of the out-of-plane magnetic anisotropy, leading to a magnetic hardening for out-of-plane magnetization. Surprisingly, the amplitude of this hardening depends strongly on the underlying substrate. While we find an increase of the coercive field around 100% for Co/Au(111), it can reach almost 600% on Co/Pt(111). Those results are discussed by using both tight-binding and ab initio calculations. It is shown on the case of C60 that both the adsorption geometry and the strain in the magnetic layer can be key ingredients to predict the quantitative change of magnetic anisotropy induced by the interface between a magnetic material and a molecular layer. On the contrary, the crystalline stacking of the Co has a minor influence.