Magnetic characterization of nano-sized iron oxide particles embedded in alginate hydrogel

We have examined the magnetic properties of a nanoparticle system (gamma-Fe2O3 alginate nanocomposite) prepared using eight iterations of a standard matrix-mediated precipitation reaction. Earlier measurements on the magnetic properties of lower generations of this system showed sensitivity to the number of iterations of the reaction[1]. We used DC magnetization measurements to determine the temperature and field dependence of the blocking temperature, saturation magnetization, and the coercive field. We find a low-field blocking temperature T$_B$=72K, higher than the lower generation samples. We probed the blocking dynamics of the system by measuring the temperature and frequency dependent complex AC susceptibility. These measurements yield a zero-field activation energy of approximately 2770K, which yields important information about the magnetic anisotropy in these systems. [1] R. Naik et al, J. Appl. Phys. (accepted for publication)