Nanostructured NdFeB films were prepared by magnetron sputtering followed by rapid thermal annealing at a ramp rate of 200 °C/s. Isotropically oriented Nd2Fe14B crystallites were formed in the films and coercivities up to 20 kOe and remanence ratios up to 0.8 were obtained. Transmission electron microscopy analysis shows that the majority phase of the magnetic layer in the high coercivity films consists of Nd2Fe14B nanocrystallites with an average size of about 50 nm. These nanocrystallites are believed to be single-domain particles, which are responsible for the high coercivities. MFM measurements show that the domain size is about 500 nm. It is thus indicated that the 50 nm Nd2Fe14B nanocrystallites are strongly exchange-coupled into the 500 nm domains and the high remanence ratio originates from this exchange coupling. © 1998 American Institute of Physics.