Phase Composition and Magnetic Properties of Nd2Fe14B/α-Fe Nanocomposites Prepared by Mechanical Alloying

Resumo

Combined studies of hard magnetic Nd₂Fe₁₄B/α-Fe nanocomposites are performed. They were prepared by mechanical alloying of melt-quenched Nd_7.4Pr_2.0Fe_76.6Co_4.2Zr_3.4B_6.4 and Nd_5.8Fe₈₀Co_4.9Ti_1.5Si_2.5B_5.3 alloys taken in mass proportions of 90/10 and 70/30. It is found that, after mechanical alloying, an amorphous–crystalline structure is formed; it consists of the hard magnetic Nd₂Fe₁₄B and soft magnetic (amorphous and α-Fe) phases. Subsequent annealing at ~500°C initiates the decomposition of the amorphous phase and the formation of the nanocrystalline Nd₂Fe₁₄B and α-Fe phases. This leads to an increase in the coercivity and the residual magnetization-to-saturation magnetization ratio (σ_r/σ_s ≥ 0.5). It is assumed that the magnetic hardening of powders is due to the formation of an exchange-coupled state, which results from the exchange interaction between α-Fe nanocrystals and the Nd₂Fe₁₄B phase.