Timopheev A. Effects of blocking and interaction in ensembles of superparamagnetic nanoparticles

The thesis deals with the investigation of influence of the blocking and interaction effects on the timing nature of magnetization reversal of ensembles of the anisotropic superparamagnetic particles. The simulations and experimental investigations were conducted in this thesis. The interrelation between these effects and measuring time has been established. The simulations were performed by different numerical methods, in particular by the new developed modeling method (recursive method), by the Monte-Carlo method and by the method of numerical solution of the differential equation which describes the process of magnetization reversal in such ensemble. As a real superparamagnetic ensembles, the nano-granular films of type "ferromagnetic metal - dielectric matrix" were experimentally investigated in this work. The comparison of results of such experimental studies with the simulation results was performed to establish influence of blocking effects and interaction effects on the magnetic properties of granular films. The complex experimental research of influence of interaction on the magnetic, transport and dynamic properties of nanogranular films exhibiting isotropic positive magnetoresistance had been conducted. It is erected that interaction influence in this film leads to formation of the state with the correlated directions of magnetic moments of granules - a superferromagnetic state which essentially modifies magnetic properties of granular system.