First-order reversal curve investigation of CoFe alloy microparticles and their microwave absorption properties

Although CoFe alloy microstructures have been widely studied for their tunable magnetic properties in applications ranging from microwave devices to biomedicine and environmental remediation, their precise magnetic behavior has not been fully elucidated so far. Here, a chemical reduction method is utilized to synthesize CoFe alloy microparticles (MPs) with variable compositions (Co_10-xFe_x, 0 ≤ x ≤ 7), followed by characterizing them using different techniques. Magnetic measurements are performed in detail by hysteresis curve and first-order reversal curve (FORC) methods. Hysteresis curves show a continuous increasing trend of saturation magnetization of Co_10-xFe_x MPs from about 72 to 173 emu/g with increasing x from 0 to 7, and a non-monotonic variation of coercivity with maximum and minimum values of 202 and 92 Oe for x = 1 and 7, respectively. Meanwhile, FORC diagrams manifest multidomain behavior of the MPs with a narrow distribution of coercive fields, which is accompanied with enhanced magnetostatic interactions for high Fe contents (x ≥ 3). Microwave absorption properties of Co₃Fe₇ alloy MPs are optimized by varying their thickness in the range of 1.4–3.0 mm, resulting in a minimum reflection loss of about –50 dB at 11.7 GHz.