Structural and magnetic properties of Joule heated Co64Fe21B15 alloy have been studied. Crystallization of the specimens starts after Joule heating with 1.6 A current, leading to the formation of nanocrystalline Co80Fe20 phase with grain diameter ranging between 19 and 25 nm. Crystallization of the specimens is found to detoriate the soft magnetic properties. Observed decrease of the hyperfine field of the amorphous component upon Joule heating suggests the increase of the boron near-neighbours to iron and the changes in the hyperfine field of the crystalline component are attributed to the changes in the environment around Fe atom in the specimen. The coercivity is found to obey a domain wall pinning process instead of random anisotropy, as expected in soft magnetic nanocrystalline magnetic materials. (C) 2011 Elsevier B.V. All rights reserved.