Synthesis of FeCo alloy magnetically aligned linear chains by the polyol process: structural and magnetic characterization

Abstract

FeCo alloy magnetically aligned linear chains (MALCs) were synthesized by the polyol process using a unique reaction format departing from conventional bench-top reactions. FeCo MALC morphology was obtained in the presence of an external dynamic magnetic field. XRD analysis confirmed the body-centered cubic (bcc) FeCo alloy. Transverse and tangential to the incident X-ray path, XRD analyses of as-synthesized FeCo MALCs were performed further substantiating the linear chain morphology. The average chain diameter was ≈206 ± 52 nm while Scherrer analysis of (110) gave an average crystallite size of 29 nm. Chemical attachment of each aligned FeCo alloy segment was confirmed by tangential cross-sectioning by a focused ion beam (FIB). Electron diffraction confirmed the bcc FeCo phase with d-spacings of (110), (200) and (211) in good agreement with XRD. The as-synthesized FeCo alloy MALCs possessed a saturation magnetization value, M_s, of 205 emu g⁻¹ and a coercivity, H_c, of 150 Oe at 300 K. Magnetization was recorded from 300 to 1000 K with increasing temperatures correlating with transitions from hcp Co/α¹ to fcc Co/α¹ at 500 K and to α¹ at 600 K for Co rich portions of the MALCs (Fe₃₂Co₆₈). Annealed (1000 K) FeCo MALCs possessed an M_s of 212 emu g⁻¹ with a H_c value of 120 Oe. Morphological changes of the 1000 K annealed sample were microwire formation and the secondary phase of cubic FeO. As-synthesized FeCo alloy MALCs as highly magnetic, air stable, non-tethered and high aspect ratio structures are candidates for radar absorbent materials (RAMs) when magnetically oriented in coatings or for magnetic sensing devices.