Nanocomposite Nd-rich Nd-Fe-B alloys: Approaching ideal Stoner-Wohlfarth type behavior

Starting from rapidly quenched NddeltaFe13.1B(2.05 less than or equal to delta less than or equal to 147.6) alloys and by appropriate annealing, the microstructure was tailored from strongly interacting Nd2Fe14B grains to magnetically isolated single domain Nd2Fe14B grains embedded in a nonmagnetic Nd-rich matrix (alpha-Nd and gamma-Nd). This change in microstructure was found to have a large effect on coercivity, i.e., coercivity, mu(0)H(c), increases with an increase of the Nd concentration from 1.25 T in Nd2.05Fe13.1B to 2.75 T in Nd147.6Fe13.1B at 290 K. Using transmission electron microscopy, the Nd2Fe14B grains in Nd147.6Fe13.1B were confirmed to be randomly oriented platelets with the c axis normal to the plate and an average size of 100 x 40 x 25 nm. For these randomly oriented, noninteracting, single domain Nd2Fe14B grains, the coercivity was calculated using a Stoner-Wohlfarth model which included the shape anisotropy of the grains. The observed coercivity of Nd2Fe14B in such nanocomposite Nd147.6Fe13.1B alloys is similar to 83% of its theoretical value. (C) 2000 American Institute of Physics. [S0003-6951(00)00513-1].