Permalloy with a body-centered-cubic structure has been grown on GaAs(001) by molecular beam epitaxy. Its magnetism, Curie temperature, and magnetic anisotropy are determined experimentally and compared to those of conventional face-centered-cubic Permalloy. Unexpectedly the vanishing magnetic cubic anisotropy in Permalloy is found to be independent of its atomic structure but depends only upon the stoichiometry of Fe and Ni in the ${\mathrm{Fe}}_x{\mathrm{Ni}}_{1-x}$ alloy. This observation is further investigated and confirmed by first-principles electronic band calculations, which help to understand the long-standing issue of why Permalloy should be a soft magnet.

• Received 13 January 2006

DOI:https://doi.org/10.1103/PhysRevLett.97.067203