Characterization of ultrasonically prepared $\gamma$-Fe$_{2}$O$_{3}$-Al$_{2}$O$_{3}$ shell-core nanocomposites

High intensity ultrasonic irradiation (sonication) of slurries of Al$_{2}$O$_{3}$ nanopowder in an Fe(CO)$_{5}$/decane mixture produce superparamagnetic $\gamma$-Fe$_{2}$O$_{3}$ shells on non-magnetic cores. In this contribution we discuss the effect of the various adjustable parameters (sonication time and intensity, powder loading, and Fe(CO)$_{5}$:decane ratio) on the dc and ac magnetic properties of these composite materials. Effects of post production modification such as heat treating powders and cold pressing pellets is also presented for a subset of samples.