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

Combined studies of hard magnetic Nd2Fe14B/α-Fe nanocomposites are performed. They were prepared by mechanical alloying of melt-quenched Nd7.4Pr2.0Fe76.6Co4.2Zr3.4B6.4 and Nd5.8Fe80Co4.9Ti1.5Si2.5B5.3 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 (σr/σs ≥ 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.