X-ray study of in-plane layer stress and orientation degree in Fe/Cr multilayers grown by MBE on R-plane sapphire

Annealing or increasing growth temperature enhance interface fluctuations, causing drastic influence on GMR and interlayer coupling. The present X-ray measurements were aimed to study the influence of the sapphire substrate temperature during MBE on the in-plane layer stress and the degree of orientation in the Fe/Cr multilayers (MLs). A series of five samples was investigated, grown in the range 60-240°C on the oriented substrate, having a Cr buffer layer in the assembly Al₂O₃/Cr(8nm)/[Fe(3nm)/Cr(1.2nm)]x8. The data were received with Cu radiation using a standard goniometer setup. At the sapphire R-plane the Fe/Cr multilayers grow in [100] direction. The orientation distribution in the layers was analyzed by rocking curves of the (200) reflection. The layer stress could be determined from the (200) reflection, measured in ML normal direction, and the perpendicularly measured reflections (020) and (002). The studies reveal that the sharpness of the (200) Fe/Cr orientation is proceedingly reduced with increasing substrate temperature. This is accompanied by a drastic relaxation of the tensile in-plane layer stress.