Ambient temperature synthesis and magnetic properties of aluminum borate-Fe nanocomposites

Nanocomposites in which fine Fe particles are dispersed in a ceramic aluminum borate AlxByOz matrix were synthesized at ambient temperatures by simultaneous hydrolysis of aluminum butoxide and reduction of Fe2+ with sodium borohydride. The nanocomposites were characterized by X-ray powder diffraction, transmission electron microscopy, SQUID magnetometry, and Mossbauer spectroscopy. The as-prepared samples consist of crystalline Fe particles dispersed in an amorphous aluminum borate matrix, which on annealing in H-2 atmosphere at T greater than or equal to 800 degrees C transforms to crystalline aluminum borate; the crystalline aluminum borate exhibits a needle-like morphology. The as-prepared samples all seem to consist of a mixture of ferromagnetic and superparamagnetic Fe particles. The superparamagnetic fraction vanishes completely on annealing in H-2 atmosphere at 900 degrees C. The magnetic results are supported by Mossbauer spectra recorded at room temperature.