The influence of intergranular interaction on the magnetization of the ensemble of oriented Stoner–Wohlfarth nanoparticles

The influence of interparticle interaction on the processes of magnetization reversal is considered for an ensemble of oriented Stoner–Wohlfarth nanoparticles. This is done through a solution of a kinetic equation describing the relaxation of the total magnetization to its equilibrium value in an effective mean field which includes a term proportional to the instantaneous value of the magnetization. It is shown that the interparticle interaction influences the temperature dependence of a coercive field. Under certain conditions, the presence of the interparticle interaction can lead to the formation of the so-called superferromagnetic state with the correlated directions of the magnetic moments of the particles. If the system is unable to come to the equilibrium during the time interval necessary to perform measurements, some measured quantities become dependent on the measurement time. It is shown that the blocking temperature Tb and the temperature dependence of coercive field at TTb, however, the coercivity, if exists, does not depend on the measurement time. The data of magnetostatic measurements, carried out on the (CoFeB)x–(SiO2)1−x nanogranular films with the concentration of ferromagnetic particles slightly lower than a percolation threshold, are in compliance with the results of the calculations.