Development of an alternative approach for electromagnetic wave absorbers using Fe–Cr–Co alloy powders

An alternative application of Fe–Cr–Co magnetic alloys as microwave absorption materials was investigated. Fe–25Cr–12Co alloy powder was spinodally decomposed at a starting temperature of 655 ℃, followed by step aging and subsequent controlled cooling to various final aging temperatures. Scanning transmission electron microscopy analysis of the step-aged samples confirmed the occurrence of spinodal decomposition. Composite samples of each step-aged Fe–25Cr–12Co powder mixed with resin were prepared to evaluate their microwave absorption properties in the gigahertz (GHz) band. We found that the imaginary component of the complex permeability for the composites could be tuned by adjusting the final aging temperature. The peak shifted from 0.3 to 3.3 GHz as the final aging temperature was reduced to 500 °C, with a minimum reflection loss of − 20 dB at 1.6 GHz. The peak shifting was ascribed to the magnetization rotation of single-domain structured ferromagnetic FeCo-rich phase particles, which was induced by the spinodal decomposition of the Fe–25Cr–12Co alloy powder to afford an FeCo-rich phase surrounded by a Cr-rich phase. The single-domain structure of the ferromagnetic FeCo-rich phase particles was generated by an increase in the compositional difference between the FeCo-rich and Cr-rich phases, which arose from controlled cooling to 500 ℃ at a rate of 5 ℃/h and holding at 500 ℃ for 10 h. This promising finding demonstrates the potential advantages of Fe–Cr–Co materials for microwave absorption applications in the GHz frequency range.