Formation and Magnetic Properties of Nanocomposites in Rapidly Solidified Fe₄₂Ni_41.7C₇Si_4.5B_3.9P_0.9 (at%) Ribbons

A novel nanocomposite structure comprising ~ 20-nm face-centered cubic Fe₅₀Ni₅₀ nanocrystals embedded within an amorphous matrix has been developed directly from a liquid alloy of Fe₄₂Ni_41.7C₇Si_4.5B_3.9P_0.9 (at%) through melt-spinning. Grain growth kinetics was significantly limited by the amorphous phase formed between nanocrystals. Glass forming elements rejected from nanocrystals stabilize the amorphous phase restricting further growth of nanocrystals. The nanocomposite ribbon exhibits excellent soft magnetic properties compared to those of the conventional micron-scale microstructured Fe₅₀Ni₅₀ alloy known as 50 Permalloy. When the as-melt spun ribbon was heated to 600 °C, two exothermic events occurred. The formation of metastable C-rich Fe₃Ni and Si- and P-rich FeNi phases at low temperatures was confirmed by detailed transmission electron microscopy analysis. The hard magnetic behaviors of these metastable phases were estimated based on the hysteresis curve analysis results obtained from a ribbon heated to 600 °C. Through proper addition of glass-forming elements to FeNi-based alloys, nanocomposites with superior soft magnetic properties were effectively fabricated for massive practical soft magnetic applications.