Magnetization curves of dipolar coupled nanomagnets

Interacting superparamagnet (ISP) model that describes the effects of dipolar coupling on the magnetizing process is examined for assemblies of anisotropic nanomagnets by controlling the coupling strength using two different methods. In the first method, the magnetic moment of each nanomagnet is grown by annealing CoAg nanogranular films. In the second method, the number density of nanomagnets in solidified iron-nitride magnetic fluids is controlled by the dilution in their melted states. Both the systems show temperature-independent magnetizing curves at lower temperatures, as predicted by the ISP model. However, in contrast to the prediction, this feature can be primarily attributed not to the dipolar coupling but to magnetic anisotropy of each nanomagnet. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.