The key methods for the preparation of magnetic nano-The key methods for the preparation of magnetic nanoparticles are described systematically. The experimental data on particles are described systematically. The experimental data on their properties are analysed and generalised. The main theoret-their properties are analysed and generalised. The main theoretical views on the magnetism of nanoparticles are considered. The ical views on the magnetism of nanoparticles are considered. The bibliography includes 416 references bibliography includes 416 references. .

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Electron paramagnetic resonance ͑EPR͒ in iron-oxide nanoparticles ͑ϳ2.5 nm͒ embedded in a polyethylene matrix reveals the sharp line broadening and the resonance field shift on sample cooling below T F Ϸ40 K. At the same temperature a distinct anomaly in the field-cooled magnetization is detected. The temperature dependences of EPR parameters below T F are definitely different than those found for various nanoparticles in the superparamagnetic regime. In contrast to canonical bulk spin glasses, a linear fall-off of the EPR linewidth is observed. Such behavior can be explained in terms of the random-field model of exchange anisotropy.

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A wide class of magnetic molecular materials - molecular clusters with high magnetic moment containing 3d transition metals (such as `Fe8', `Mn12ac', etc) - have been considered from the point of view of their use as refrigerants in low-temperature regions. The consideration was made in the framework of the model based on the Langevin theory of a superparamagnet. The magnetic entropy change caused by a change in an external magnetic field was calculated for various magnetic clusters. The estimations made show that the magnetic molecular clusters could be promising materials for magnetic refrigeration in low-temperature regions (below about 20 K).