Influence of heat treatment, near the temperature region of Fe α-γ transformation, on the interphase exchange coupling of Nd2Fe14B + Fe nanocomposites

Hard-Soft Exchange coupled nanocomposite magnets rely on a precise control of both crystal structure and microstructure for the constituent phases. In Nd₂Fe₁₄B + 10 wt%α-Fe magnetic nanocomposites obtained through mechanical milling, the nanostructure refinement is achieved by annealing for a short duration. This work builds upon previous results in two ways: (i) increasing rapid annealing temperature and rate, (ii) taking advantage of the Fe α/γ transformation in order to limit the growth of the soft phase crystallites. Annealing was performed at temperatures between 800 °C and 950 °C under purified inert He gas for durations between 38 s and 65 s. The structure and microstructure of the nanocomposites were studied through XRD and SEM, while their magnetic properties and the effectiveness of the interphase exchange coupling were studied using demagnetization curves (±10 T) and dM/dH plots.