Thickness effects on microstructure, mechanical and soft magnetic properties of sputtered FeZr thin film metallic glass

In this work, we report the thickness effects on microstructure, mechanical and soft magnetic properties of Fe75Zr25 thin film metallic glasses (TFMGs) prepared by DC magnetron sputtering. The Fe75Zr25 TFMGs exhibit a nano-granular structure and the particle size is growing with the increase of thickness. The hardness (H) and the elastic modulus (E) evaluated by nanoindentation, both show a decreasing trend with the increase of film thickness. The smooth P-h curves reflect a homogenous deformation mode, which is attributed to the activation of shear transformation zones (STZs) in the nanoscale granular thin films that could reasonably restrain the formation of shear bands. Furthermore, a positive strain rate dependence was observed for all films with highest strain rate sensitivity SRS (m) value of 0.037 for thicker film, more likely due to the free volumes accumulation during deformation. In addition, Fe75Zr25 TFMGs show anomalous strong ferromagnetism at low and high temperatures (10 K and 300 K). It is found that in a critical thickness of 270 nm, the Fe75Zr25 TFMGs manifest the desired combination of soft magnetism and mechanics. The underlying mechanism of variation in mechanical and soft magnetic properties could be rationalized in light of the interplay of nanoscale granular size and structural evolution with increase of film thickness. This study offers a paradigm to design Fe-based TFMGs with simultaneously superior mechanical performance and excellent soft magnetic properties.