Effects of aging at room temperature on as-spun Nd2Fe14B/α-Fe nanocomposite magnets

As-spun exchange-coupled Nd-Fe-B-X (X=In, Ti) nanocomposites were prepared by using the melt-spinning method. Effects of aging at room temperature on magnetic behaviors of the as-spun powders were investigated. It was found that both coercivity Hc and reduced remanence mr are significantly enhanced as a result of short-range atom diffusion and stress relaxation at the intergranular region, rather than of grain growth or crystallization of amorphous phase, after being stored for a long time at room temperature (0-35 °C). Enhancements reach a maximum when amorphous and crystalline phases coexist in nanocomposites. XRD results indicate that a transitional Nd2Fe14B-like intergranular phase may be formed or developed near grain boundaries during the aging process. It is a more crystallographically coherent, stress relaxed, and chemically balanced intergranular region that is very beneficial to the promotion of intergrain exchange coupling and hardening between adjacent magnetic soft and hard grains. The role of the intergranular phase in magnetic exchange coupling and hardening mechanisms is also discussed in this paper.