Fabrication of spin valve junctions based on Fe/Fe$_{3}$Si/FeSi$_{2}$/Fe$_{3}$Si quadrilayered films by facing targets direct-current sputtering*

In order to prepare magnetic multilayered films applicable to spin devices, the film preparation method is an important key that determines the quality of the spin devices, such as interfaces between layers and crystalline orientations. A facing targets direct-current sputtering (FTDCS) method, in which a couple of targets are positioned in parallel and a substrate is set in the direction perpendicular to the two targets, has the following features: (i) less plasma damage, (ii) fewer rises in the substrate temperature, and (iii) small stoichiometric differences between the target and film, owing to a substrate is free of the plasma. These features should be beneficial to Fe$_{3}$Si/FeSi$_{2}$ multilayered films at low substrate temperatures, with Fe$_{3}$Si and FeSi$_{2}$ sintered targets. In this study, Fe/Fe$_{3}$Si/FeSi$_{2}$/Fe$_{3}$Si multilayered films were prepared by employing the FTDCS method. The bottom Fe$_{3}$Si layers were epitaxially grown on Si(111) substrates, and they exhibited small coercive forces of less than 10 Oe. Posterior to FeSi$_{2}$ layers being deposited on the bottom Fe$_{3}$Si layers, polycrystalline Fe$_{3}$Si and Fe were successively deposited on the FeSi$_{2}$ layers. The resultant multilayered films showed sharp signals due to magnetoresistance as spin valves.