Ultrahigh Saturation Magnetization in Fecob Powders with Controllable Amorphous-Nanocrystalline Structure Via the Synergism of Deformation and Energy Injection

Abstract

Amorphous-nanocrystalline magnetic powder cores (ANMPCs) are highly potential soft magnetic materials in high-frequency applications of power electronic devices. However, their relatively low saturation magnetization cannot satisfy the miniaturization of devices. Strong FeCo exchange coupling amorphous-nanocrystalline powder is a promising candidate to prepare the required ANMPCs. In this work, a series of (Fe0.8Co0.2)87B13 soft magnetic powders with controllable content of amorphous and nanocrystalline phases and tunable particle size were fabricated by mechanical ball milling of pure Fe, Co and B powders. During the ball milling procedure, the three-stages vitrification and nanocrystallization combined with morphology and size developments were revealed, leading to the nonmonotonic variation of soft magnetic properties. The combination of ultrahigh saturation magnetization of 239 emu/g and moderate effective permeability of 33 was achieved in the milled magnetic powders. After milling for 150 h, the FeCoB powder reaches a dynamic equilibrium manifesting as the nano-to-micro scale particle size and a stable amorphous-nanocrystalline dual-phase structure, which results in the improvement of high-frequency stability and core loss. With the synergism of deformation and energy injection, the mechanical ball milling is an effective way to realize the controllable nanocrystallization of amorphous powders containing ultimate ferromagnetic elements and improve the comprehensive soft magnetic properties of ANMPCs.

Keywords: Amorphous-nanocrystalline magnetic powder core, Mechanical ball milling, Ultrahigh ferromagnetic element, Saturation magnetization, High-frequency properties