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 de lta less than or equal to 147.6) alloys and by appropriate annealing, the m icrostructure was tailored from strongly interacting Nd2Fe14B grains to mag netically isolated single domain Nd2Fe14B grains embedded in a nonmagnetic Nd-rich matrix (alpha-Nd and gamma-Nd). This change in microstructure was f ound to have a large effect on coercivity, i.e., coercivity, mu(0)H(c), inc reases with an increase of the Nd concentration from 1.25 T in Nd2.05Fe13.1 B to 2.75 T in Nd147.6Fe13.1B at 290 K. Using transmission electron microsc opy, the Nd2Fe14B grains in Nd147.6Fe13.1B were confirmed to be randomly or iented 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 doma in Nd2Fe14B grains, the coercivity was calculated using a Stoner-Wohlfarth model which included the shape anisotropy of the grains. The observed coerc ivity of Nd2Fe14B in such nanocomposite Nd147.6Fe13.1B alloys is similar to 83% of its theoretical value. (C) 2000 American Institute of Physics. [S00 03-6951(00)00513-1].