Figure 5.

Zero field cooled/field cooled (ZFC/FC) measurements show a shift of the blocking temperature T_B to lower temperatures with decreasing concentration, which can be explained by less interaction between the particles.T_B indicates the transition between ferro- and superparamagnetic behaviour. The broadening of the peak is not caused by inhomogeneous particle size distribution but by magnetic interactions between the particles. The initial concentration of the particle solution has been diluted with hexane till a 50% solution of the initial one has been reached