Effect of Seed Layers on Polycrystalline Thin Films

We report on the control of grain development and its effect on magnetic properties in polycrystalline Co₂FeSi thin films through use of Ag layers. Thin film polycrystalline samples consisting of a 20 nm Co₂FeSi layer deposited onto a 6 nm Ag seed layer have been fabricated using high target utilization sputtering. After thermal annealing at 300°C for 6 hours these films have median grain diameters of between 30 and 40 nm which are constrained by island like growth of the Ag Seed layer. This constraint of grain growth results in films with coercivities of no greater than 40 Oe and values of saturation magnetization exceeding 80% of the theoretical bulk value. The use of Ag seed layers is thus shown to reduce coercivities by almost 90% compared with previously reported similar materials making them much more suitable for device applications.