Alloys of Fe49Co49V2(Hiperco Alloy 50) (Hiperco is a registered trademark of CRS Holdings, Inc.), both annealed and thermally aged, were studied using anomalous synchrotron x‐ray and neutron powder diffraction. Rietveld and diffraction profile analysis indicated both anincreasein the structural order parameter and a small latticeexpansion(∼0.0004 A˚) after aging at 450 °C for 200 h. In addition, a cubic minority phase (<0.3%) was identified in the ‘‘annealed’’ sample, which increased noticeably (0.3%→0.8%) as a result of aging. The presence of antiphase domain boundaries in the alloys was also revealed. These results directly correlate with the observed changes in the magnetization behavior and challenge the notion that a ‘‘fully’’ ordered Fe–Co alloy demonstrates optimum soft magnetic properties. ©1996 American Institute of Physics.