Magnetic methods of structural analysis of nanocrystalline alloys - Magnetic granulometry

Non-conventional, two phase granular magnets composed of magnetic crystallites embedded in amorphous matrix, magnetic as well, are presently widely applicable in electronics owing to their extremely good magnetic softness. They are produced by devitrification of rapidly quenched metallic glasses performed under well controlled annealing conditions. Besides of the practical importance, these granular magnets also become excellent objects for the basic research on magnetism. Depending on the composition of the parent material, size and volume content of the crystallites and also on the temperature of measurements, they show a variety of magnetic phase. Additionally, because of nanometer size of crystallites, their surface to volume ratio is very large allowing to expect novel properties not occurring in the bulk magnetic materials (magnetic atoms on the surface reveal different symmetry than those in the bulk). To study of the mentioned magnetic phenomena, granular structure of nanocrystalline magnets must be known (size of the crystallites and its distribution, their volume content as well as the composition). All these parameters can be calculated applying magnetic methods if only the studied material fulfills the conditions at which the superparamagnetic behaviour of the crystallites can occur. The procedures applied to calculate structural parameters will be exemplified using granular magnet comprising of Fe(Si) nanocrystallites embedded in the residual amorphous matrix of the initially FeCrCuNbSiB metallic glass. The results obtained this way will be compared with those given by conventional methods (TEM and X-ray diffraction). (author)