NMR and Mössbauer study of peculiarities of the structure formation in Fe–Сo alloys

Fe–Co alloys with an Fe content of 20–95 at % have been investigated using NMR and Mössbauer spectroscopy. A comparison of the hyperfine fields measured at 59Со and 57Fe nuclei on the same samples allowed us to determine that the magnetic moment at an Fe atom in the disordered alloys with Fe concentrations of 20–80 at % varies from 2.8 to 2.4 μB, as well as to ascertain peculiarities of the formation of an ordered state. The data obtained indicate the existence of regions with a short-range order of the D03 type in alloys with an Fe content of 70–80 at %. In alloys with iron concentrations greater that 80 at %, the phase separation of the structure into regions of elemental iron and short-range-ordered Fe89Co11 regions is observed. The obtained results explain the contradictions in the values of the magnetic moment at the Fe atom and the anomalous dependence of the lattice parameter of the alloy with a Со content less than 20 at %, as well as prove the accuracy of the phase diagram containing regions of three bcc phases, rather than one, as is commonly accepted.