Chemical synthesis, microstructure, and magnetic properties of chains composed of ultrafine Fe-Co-B particles

An inexpensive chemical method was used to obtain ferromagnetic chains composed of nanometer size spheres of Fe-Co-B. The method involves a controlled reduction with KBH4 in aqueous as well as water-ethanol media of Fe2+ and Co2+ in the presence of an applied magnetic field. The chemical composition, particle size, crystallinity, and microstructure are characterized by inductively coupled plasma analysis, transmission electron microscopy, and x-ray diffraction. The magnetic properties are evaluated with superconducting quantum interference device magnetometer. The particle size and crystallinity decrease by increasing both the Co content and the amount of ethanol in the reaction medium. The observed magnetic properties are correlated to the degree of crystallinity and chemical composition. The magnetic properties are improved significantly by a subsequent annealing step at 400-500 degrees C in an Ar-H-2 mixture. Moreover, the experiments carried out to verify the magnetization reversal mechanism support the chain of spheres model. (C) 1996 American Institute of Physics.