Magnetic states of iron in metastable fcc Fe-Cu alloys

X-ray magnetic circular dicroism at the K absorption edge of iron is exploited to elucidate the local spin structure of Fe in metastable, ferromagnetic fcc Fe-Cu alloys. At Fe concentrations as high as 50 at.%, Fe-Cu alloys are particularly suitable for studying the magnetic state of iron in an fcc environment, because of the negligible contribution of copper to the alloy magnetic moment. The experimental spectra are consistent with the picture of iron atoms coexisting in two different magnetic moment states and point out at the negative sign associated with the low magnetic moment state. This result brings in more evidence on multiple magnetic states, simultaneously present in 3d alloys with competing ferromagnetic and antiferromagnetic interactions, and offers a common explanation to the Invar effects recently reported for the Fe-Cu system.