# Magnetic Properties of Nanocomposites
###### Abstract  
The magnetic properties of various families of nanocomposite materials containing nanoparticles of transition metals or transition-metal compounds are reviewed here. The investigated magnetic nanocomposites include materials produced either by dissolving a ferrofluid containing pre-formed nanoparticles of desired composition and size in a fluid resin submitted to subsequent curing treatment, or by generating the nanoparticles during the very synthesis of the embedding matrix. Two typical examples of these production methods are polymer nanocomposites and ceramic nanocomposites. The resulting magnetic properties turn out to be markedly different in these two classes of nanomaterials. The control of nanoparticle size, distribution, and aggregation degree is easier in polymer nanocomposites, where the interparticle interactions can either be minimized or exploited to create magnetic mesostructures characterized by anisotropic magnetic properties; the ensuing applications of polymer nanocomposites as sensors and in devices for Information and Communication Technologies (ICT) are highlighted. On the other hand, ceramic nanocomposites obtained from transition-metal loaded zeolite precursors exhibit a remarkably complex magnetic behavior originating from the simultaneous presence of zerovalent transition-metal nanoparticles and transition-metal ions dissolved in the matrix; the applications of these nanocomposites in biomedicine and for pollutant remediation are briefly discussed. nanocomposites; magnetic nanoparticles; superparamagnetism; polymers; ceramics; sensors; biomedicine; environment +
Footnote †: journal: Applied Soft Matter  
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NP magnetism [4; 5]. Some aspects are still unclear, such as the extent to which the interface between magnetic NPs and a given matrix influences their properties [6; 7]. Although the basic principles of nanomagnetism have been long since established [8], a general predictive picture of the magnetic properties of a given NC, or a family of NCs, is still lacking. This is because a number of ill-known parameters hinder the knowledge of the physical processes at the nanoscale and affect the interpretation of the measured magnetic properties. On the other hand, in view of the applicability of magnetic NCs, the need for easy, cheap, and eco-sustainable preparation and processing is a central issue; another challenge concerns the stability in time and the disposal at the end of life (EOL) of these materials [9; 10]. Often, the differences in magnetic behavior found in different magnetic NCs are ascribed to contrasting morphologic features, such as nature of the particle size distribution (e.g., monodisperse vs. polydisperse particles) and degree of particle coupling (e.g., independent vs. interacting particles, or isolated vs. aggregated particles). However, remarkable differences among final products may be directly related to the nature and features of the preparation procedure. In this respect, two main strategies can be envisaged: in one case, the magnetic NPs are first prepared as a nanopowder by means of a suitable chemical route, and subsequently dissolved by mixing/stirring in an initially fluid host, which finally becomes a solid through an appropriate process (a typical example being polymer NCs obtained by suitably curing a fluid resin loaded with a dispersion of magnetic NPs) [11; 12; 13]; alternatively, the magnetic particles and the solid host matrix can be simultaneously obtained (a typical example being ceramic NCs obtained by thermal treatment of a transition metal-loaded zeolite precursor) [14].