Crystallization Behavior of Chemically Prepared Nanoparticles of Amorphous Fe-B*

The crystallization behavior of amorphous Fe-B nanoparticles prepared by reducing an aqueous solution of Fe$^{+2}$ ions with NaBH$_{4}$ has been studied by differential scanning calorimetry (DSC), vibrating sample magnetometry (VSM), and x-ray diffraction (XRD) measurements. At a heating rate of 10 \r{ }C/min the DSC measurements show a sharp and well defined exothermic peak at a temperature of about 475 \r{ }C and a Kissinger analysis of the shift in the position of this peak as a function of the heating rate yields an activation energy of about 3.6 eV/at. The VSM measurements also exhibit a sharp increase in the magnetization at a temperature 475 \r{ }C (at a heating rate of 10 \r{ }C/min). X-ray diffraction measurements on samples heated to temperatures slightly above 475 \r{ }C verify that the observed DSC and VSM signals correspond to the transformation from the as-prepared amorphous structure to a crystalline structure. * This work has been supported by AFRL DARPA METAMATERIALS contract no. F33615-01-2-2166, ARO DEPSCOR grant no. W911NF-04-1-0264, and the Undergraduate Research Program at the University of Delaware.