03-18U

Assuming that the magnetic properties of lava-like fuel-containing materials are caused by the magnetism of small nanoparticles, immersed in glass-like matrix, we analyze the main specific features in magnetic behavior which can be observed experimentally. Basic principles of theoretical description and experimental investigations, being useful for the verification of such hypothesis, are discussed. The properties of a system, consisted of single-domain nanoparticles, are analyzed in dependence on an external magnetic field and experimental setup. The main ideas for theoretical study of such systems within phenomenological or/and microscopic schemes are considered with the emphasis on different physical mechanisms and processes.