ABSTRACTWe studied the effects of phosphorus (P) on Ni nanocrystalline morphology formed by focused ion beam (FIB) irradiation for Ni-P amorphous alloy thin films. The P content in the amorphous alloy was varied from 8 to 12 wt.%. The nanocrystals induced by the FIB irradiation for Ni-11.8, 8.9, 7.9 wt.% amorphous alloy had an f.c.c. structure and showed unique crystallographic orientation relationships to the geometry of the focused ion beam, that is, {111}f.c.c. parallel to the irradiated plane and <110>f.c.c. parallel to the projected ion beam direction, respectively. The Ni nanocrystals precipitated like aggregates with decreasing of the P content. These results represent that the P content does not affect crystallographic orientation relationships, while influences the precipitation distribution of Ni nanocrystals generated by the FIB irradiation.