Nanoimprinting of magnetic FeCo-based metallic glass thin films

The ability to create submicron/nanoscale patterns with magnetic alloys at low cost is difficult. Here, we demonstrate a method to create such patterns using Fe₄₀Co₃₅P₁₀C₁₀B₅ metallic glass thin films. The viscous workability of a metallic glass thin film was used to make patterns with dimensions up to ~100 nm using the nanoimprinting technique, and the effects of the patterning on the magnetic properties of the metallic glass thin films were investigated. An increase in the out-of-plane coercivity (~380 Oe) and remanent magnetization (M_r = ~12% of the saturation magnetization, M_s) were observed for amorphous thin films patterned with a high density of nano-dots. This effect was observed because of changes to the magnetic shape anisotropy induced by the nano-imprinting. Two events of magnetization reversal were confirmed in the crystalline films of the same alloy. The reversal of magnetization under the low magnetic field of ~100 Oe corresponds to soft magnetic phases, whereas that at 2400 Oe corresponds to the hard magnetic phase. Recoil curve measurements suggest that the average magnetization-switching field of hard magnetic grains in the film was between 2800 and 3600 Oe. Based on our experimental results and analysis, we suspect the presence of tetragonal Fe–Co hard/semihard magnetic phase in crystalline thin films. We believe that the low-cost and large-area micro- to nanoscale patterning ability of the present magnetic thin films are promising for the development of various magnetic MEMS and memory devices.