Magnetization experiments on frozen ferrofluids

Ensembles consisting of Co nanoparticles fixed in space by freezing ferrofluids are investigated. In frozen ferrofluids a well defined low temperature magnetic state of the nanoparticle system can be achieved. We distinguish between textured samples (preferred orientation of easy axes) and non-textured with randomly oriented easy axes. Considering the magnetization curves of such systems bears in principle the possibility to distinguish between influences arising from particle anisotropy and particle-particle interaction. Our intention is to present new experimental strategies aiming to separate these influences from magnetization measurements versus temperature. In another approach we analysed the susceptibility derived from magnetization measurements and determined the mean magnetic moment of the particles and an additional field which may be caused by the anisotropy of the particles or the interaction between them. Transmission electron microscopy was used for the direct measurement of the particles' sizes and their size distribution.