Experimental study of ferromagnetic chains composed of nanosize Fe spheres

Chains composed of nanometer size spheres of Fe have been synthesized by a controlled reduction at ambient temperature of aqueous ${\mathrm{Fe}}^{2+}$ with ${\mathrm{KBH}}_4$ in the presence of an applied magnetic field. The chains are characterized by x-ray diffraction, transmission electron microscopy, and superconducting quantum interference device magnetometry. The size of the crystalline Fe spheres could be varied from 20 to 70 nm by controlling the synthesis conditions. The magnetization reversal behavior of these chains are examined and compared with the theoretical predictions of the ‘‘chain of spheres model.’’ The observed values of the coercive force ${\mathit{H}}_{\mathit{c}}$, variation of ${\mathit{H}}_{\mathit{c}}$ with particle size, relationship between the ${\mathit{H}}_{\mathit{c}}$ values of randomly oriented and aligned chains, remanence of randomly oriented chains, and angular dependence of ${\mathit{H}}_{\mathit{c}}$ in the single-domain region are all in support of a symmetric fanning mechanism for magnetization reversal. This study represents an example of fabrication of a true chain of spheres and comparison of their magnetic properties with theoretical predictions available in the literature. © 1996 The American Physical Society.