Role of Cu Doping in Augmenting Sluggish Interdiffusion in Fe/Ni Multilayers

The interdiffusion between Fe and Ni is sluggish, and in order to synthesize the technologically important L1 0 ‐ordered FeNi phase, it needs to be boosted. Cu doping is expected to create a disorder, leading to an enhancement in interdiffusion. Therefore, during the growth of Fe/Ni multilayers (MLs) by the sputtering process, Cu is cosputtered, and its amount is varied nominally at 5, 10, and 15 at% by tuning the sputtering power of Cu source. The interdiffusion is studied using polarized neutron reflectivity (PNR) of annealed Fe/Ni ML samples. Resulting FeNi phases are analyzed using X‐ray diffraction. Both PNR and a magnetometer are used to study the magnetization, and the surface morphology is studied using atomic force microscopy. It is found that the lowest amount of doping at 5 at% is the most effective in accelerating the interdiffusion, but as the amount of Cu doping is further increased, the interdiffusion again becomes sluggish due to excessive grain boundary segregation and clustering of Cu. These findings highlight the importance of controlling the Cu doping concentration to promote the interdiffusion, leading to the realization of the formidable L1 0 FeNi phase.