Study on magnetic properties and microstructure of Fe0.18Co0.36Ni0.21Al0.10Cr0.15 high entropy alloy thin films

Abstract

High entropy alloys (HEAs) based on magnetic elements (Fe, Co, Ni) are expected to show excellent soft magnetic properties and good electrical and mechanical properties. In this study, Fe0.18Co0.36Ni0.21Al0.10Cr0.15 HEA films of two different thicknesses (20 nm, 175 nm) have been prepared by magnetron sputtering method using pure metal targets. The magnetic measurements show that the as-deposited films have low saturation magnetization (247 emu/cm3) but increase with increasing annealing temperature. It shows a maximum value of 698 emu/cm3 when annealed at 800 ℃. At the same time, the coercivity (Hc) changes from 3 to 87 Oe. The XRD results have shown that the as-deposited films have a single-phase FCC (111) structure. With the increase of annealing temperature, the crystallinity becomes better, but there is no phase transformation. The transmission electron microscopy (TEM) results further confirmed the formation of a uniform FCC phase. Increasing the annealing temperature facilitates the growth of grains, which is the main reason causing the change of coercivity. Element mapping results have revealed that at room temperature, the distribution of the five elements is uniform, whereas after annealing at 400 ℃, Fe and Co slightly segregate. When the film is annealed at 600 ℃, antiferromagnetic element Cr has apparent segregation, while other elements do not segregate apparently, which promotes the increase of saturation magnetization (Ms). The films show high resistivity (110–120 μΩ⋅cm) and good mechanical properties, even after annealing at 800 °C, showing excellent thermal stability.