Effect of Co Vacancies on Structural and Magnetic Properties of Co₂TiSn Heusler Alloy Thin Films

Co-based Heusler alloys have attracted significant attention for spintronic and magnetoelectronic applications due to their high spin polarization, tunable electronic structure, and robust magnetic properties. However, achieving the desired spin polarization and atomic ordering in thin films is highly sensitive to stoichiometry and growth conditions. In this study, we deposited high-quality epitaxial thin films of CoₓTiSn (x = 2.0, 1.75, and 1.5) on both a- and c-plane sapphire substrates with TiN buffer layers using sputter beam epitaxy. Remarkably, we observe that even with reduced Co content, the films maintain a well-defined epitaxial cubic Heusler structure, indicating strong structural stability against Co deficiency. By systematically varying the Co concentration, we investigate how deviations from stoichiometry affect the structural stability, magnetic ordering, and electronic properties of these alloys. We will discuss the growth process, as well as the evolution of structural and magnetic behavior as a function of both Co concentration and film thickness, providing insight into the compositional and dimensional control of Co-based Heusler thin films.