Conditions of phase transitions in systems of identical ferromagnetic spherical nanoparticles randomly distributed in metal nonmagnetic matrix and superlattices of small number of nanoparticles with the Ruderman-Kittel-Kasuya-Yosida interaction are researched. In the framework of the Ising model the behavior of superspins is well described with the random interaction field method. The alteration of the effective magnetic moment due to the change in volume affects the choice of the magnetic state of the system: ferromagnetic spin glass or antiferromagnetic spin glass. The ground state of superlattice depends on the distance between particles.
In this investigations the systems of the nanoparticles with competing exchange interactions are considered. The critical concentrations and possible types of magnetic states of particles in the case of direct exchange and RKKY interaction in the framework of the random interaction field method are determined. It is observed that in magnetic materials with the competition of the direct and indirect exchanges changing the type of ordering is possible at the change in the intensity of the indirect exchange under the influence of external factors.
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