Effects of magnetic seed-layers on the structural and magnetic properties of Co ₂MnSi Heusler alloy

We investigated the structural and magnetic properties of Co ₂MnSi deposited on Co ₉₀Fe ₁₀ and Co ₅₀Fe ₅₀ ferromagnetic seed-layers at room temperature before and after annealing at various temperatures up to 500 °C. The lattice misfits between Co ₂MnSi and Co ₉₀Fe ₁₀ and between Co ₂MnSi and Co ₅₀Fe ₅₀ were expected to be 2.0% and 0.5%, respectively, which are small enough to allow an epitaxial relation or to promote a texture between layers. The Co ₂MnSi grown on the Co ₉₀Fe ₁₀ seed-layer transformed from an A2 to a B2 structure when it was annealed at a temperature as low as 350 °C, evidenced by the (200) peak. The transformation of the Co ₂MnSi to an L2 ₁ structure did not take place until it was annealed at 500 °C. The soft magnetic properties of the Co ₂MnSi on the Co ₉₀Fe ₁₀ were substantially improved. In contrast, the Co ₂MnSi prepared on the Co ₅₀Fe ₅₀ seed-layer did not transform to L2 ₁ even after annealing at 500 °C. Instead, it showed a B2 structure. The Co ₉₀Fe ₁₀ and Co ₅₀Fe ₅₀ ferromagnetic seed-layers found to be useful not only to facilitate the transformation to ordered phases but to improve the soft magnetism of Co ₂MnSi, which makes feasible for the use of Co ₂MnSi in applications such as magnetic read heads, magnetic random access memories, and spin transistors.