Interfacial effects in manganite thin films with different capping layers of interest for spintronic applications

We report on the use of surface-sensitive techniques (x-ray absorption spectroscopy and x-ray magnetic circular dichroism) to investigate interfacial effects in sputtered manganite thin films, La2/3Ca1/3MnO3 (LCMO) and La2/3Sr1/3MnO3 (LSMO), with different capping layers [MgO, LaAlO3 (LAO), SrTiO3 (STO), NdGaO3 (NGO), and Au]. To ensure surface sensitivity, data were acquired by using the total electron yield detection mode. It is found that LSMO and LCMO films exhibit similar behavior when capped with oxide layers but dissimilar effects when a metallic capping is used. Almost bulklike Mn valence at the interface was observed in the case of LAO capping. However, a notorious increase of the Mn oxidation state was detected for both MgO and NGO capping layers. In contrast, metallic Au and STO capping promotes a reduction of the Mn oxidation state. These results are correlated with the x-ray magnetic circular dichroism data, showing a concomitant decrease of the saturation magnetization at the interface in those cases where a modification of the Mn oxidation state is observed.