CONICET | Buscador de Institutos y Recursos Humanos

A model is developed with the aim of analyzing relevant aspects of systems ofinteracting magnetic nanoparticles. Model is built from magnetic dipolarinteraction and demagnetizing field concepts. By making reasonable simplifyingapproximations a useful expression for effective demagnetizing factor N isachieved, which allows for the analysis of uniform or non uniform spatialdistributions of nanoparticles, i.e. for the occurrence of clustering. Thisexpression is a function of demagnetizing factors associated with specimen shapeNs and average cluster shape Nc, and of the mean relative distances betweennanoparticles γ=d/D and clusters γc=dc/Dc,N=(φ/γ3)(Nc(1-1/γ3)+Ns φc/γc3),where D, Dc and d, dc are mean nanoparticle/cluster sizes and meannanoparticles/clusters near neighbor distances, respectively. φ and φc are packingfactors adequately defined to consider NPs and clusters spatialdistributions. Average magnetic dipolar energy per nanoparticle can be estimatedas a function of D, N and magnetization.Experimental M(H) results from rectangular prism specimens consistent ofdispersions of polyacrilic acid coated magnetite nanoparticles in PVA hydrogels,with mass fractions Xm between 0.014 and 0.093, are presented and analyzed withthis model. Analysis clearly demonstrates the influence of prism relativedimensions on the recorded low field susceptibility and on the size of nanoparticlemagnetic moment retrieved from magnetic measurements, therefore highlightingthe importance of reporting complete information on measurement geometry. Italso shows the occurrence of clustering and permits the retrieval of significantstructural information. It was found that clusters are randomly oriented and γc varied with Xm, from 4.7 to 2.5 while γ remained almost constant at 1.4. Usingmodel expressions, properties corresponding to non interacting nanoparticles,such as magnetic susceptibility and magnetic moment could be retrieved