Three‐dimensional elemental mappings of Co–Cr–Ta thin film sputter‐deposited at 200 °C were obtained using a three‐dimensional atom probe. We have confirmed that Ta atoms are dissolved in the film homogeneously, and no segregation of Ta was found at the grain boundaries. On the other hand, Cr atoms are inhomogenously dissolved within grains, and it is strongly enriched at the grain boundaries forming a Cr‐enriched grain boundary phase with a thickness of approximately 4 nm. ©1996 American Institute of Physics.