  Initial powder mixtures of Cu, Fe and Co are exposed to severe plastic
deformation by high-pressure torsion to prepare solid solutions. A broad range
of compositions is investigated, whereas this study aims at the synthesis of
soft magnetic materials and therefore at the formation of a homogeneous and
nanocrystalline microstructure. For intermediate ferromagnetic contents,
high-pressure torsion at room temperature yields single-phase supersaturated
solid solutions. For higher ferromagnetic contents, two consecutive steps of
high-pressure torsion deformation at different temperatures yield the desired
nanocrystalline microstructure. Depending on the Co-to-Fe-ratio, either a
single-phase supersaturated solid solution or a nanocomposite forms. The
composite exhibits an enhanced magnetic moment, indicating the formation of a
(Fe,Co)-alloy upon severe plastic deformation. Soft magnetic properties are
verified for large Co-to-Fe-ratios and this microstructure is found to remain
stable up to 400 {\deg}C.
