Enhancement of the exchange coupling interaction of nanocomposite Nd2Fe14B/α-Fe magnets by a small amount of Sm substitution for Nd

Nanocomposite Nd2Fe14B/α-Fe magnets show exchange-coupled permanent magnet properties if the sizes of both Nd2Fe14B and α-Fe phases are of the order of twice the domain wall width of the hard Nd2Fe14B phase, which is about 10 nm. It is very difficult to control the grain sizes (especially the size of α-Fe phase) below 10 nm, because nanocomposite Nd2Fe14B/α-Fe magnets are usually synthesized by melt spinning and subsequent crystallization annealing. So, the exchange coupling interaction between the hard and soft phases will become reduced. Here, we reported the enhancement of the exchange coupling interaction of nanocomposite Nd2Fe14B/α-Fe magnets by a small amount of Sm substitution for Nd. For the pure Nd8Fe86B6 ribbons, the soft α-Fe particles are not exchange-coupled to the hard 2:14:1 phase when the mean grain size of α-Fe phase reaches 18.3 nm. But for the Nd7.8Sm0.2Fe86B6 ribbons, the soft α-Fe phase is exchange-coupled to the hard 2:14:1 phase even if the mean grain size of the α-Fe phase exceeds 22.4 nm. This can be attributed to an extension of the exchange coupling range by reducing the magnetocrystalline anisotropy of the hard Nd2Fe14B phase.