Tailoring the magnetic properties of Fe_xCo_(1-x) nanopowders prepared by a polyol process

Precise control over the magnetic properties of FeCo alloys is of scientific significance, due to their high Curie points and saturation magnetizations, and of broad interest for applications such as transformer cores, induction motors, switching devices, and hyperthermia. The magnetic properties of Fe_xCo_(1-x) alloy-based nanopowders prepared by polyol synthesis and their relationship with morphological features and the evolution of the microstructure were investigated using a design of experiments (DoE) approach. Proportionalities related to the magnetic properties, saturation magnetization (M_s) and coercivity (H_c), were identified where M_s ∝ (110) crystallite size of FeCo (bcc) and H_c ∝ particle diameter for the as-synthesized Fe_xCo_(1-x) nanopowders. Adjusting the reaction composition allows for control of the FeCo (bcc) (110) crystallite size from 20-45 nm represented by a response surface model. Morphological features of the as-synthesized nanopowders include particles interlinked as chains, and particles either in the form of cuboids or spheroids, all with diameters ranging from 75-175 nm. Fe_xCo_(1-x) alloy was confirmed by XRD in each nanopowder while few contained a combination of phases which include Co (fcc), or ferrite (CoFe₂O₄), or both. Depending on composition, particle dimension, and microstructure, the M_s ranged from 90-215 emu g^-1 with H_c from 90-400 Oe for all nanopowders synthesized by the sub-reflux, isothermal condition (150 °C). Tailoring the magnetic properties of Fe_xCo_(1-x) alloy-based nanopowders is accomplished chemically by identifying and regulating significant reaction parameters and conditions.