Tykhonenko-Polishchuk Y. Static and dynamic magnetic properties of spinel ferrite and substituted manganite nanoparticles

The work is aimed at the investigation of the characteristic changes in static and dynamic magnetic properties of spinel ferrite and substituted manganite nanoparticles under the influence of the chemical substitutions and conditions of the synthesis, using the various model approaches for the comprehensive analysis of their magnetic state in terms of parameter distribution of real nanoparticle ensembles. The carried out research deals with the modern physical problems of nanoscaled objects. Key parametric factors and the ways toward the optimization of the high-frequency thermal efficiency have been investigated for the spinel ferrites (Ni, Zn, Co, Mn)Fe2O4. It has been found that the synthesis of nanoparticles with an optimal quasistatic blocking temperature of ~ 90 K could increase the energy losses by two orders of magnitude, in comparison with the values obtained in recent experiments. The transformation peculiarities of the magnetic state caused by the chemical substitutions in the lanthanum sublattice and the conditions of chemical synthesis have been determined for the substituted manganites La_{0,7-x}(Nd, Sm)_xSr_{0,3}MnO_3 (x = 0 - 0,1). The magnetic parameters (magnetization and Curie temperature, T_C) of the nanoparticles have been determined, the driving factors and peculiarities of their evolution have been disclosed and proved. On the basis of numerical simulations of the magnetization curves at different temperatures and their comparison with the experimental data, the nature of the magnetic state for inhomogeneous ensembles of manganite nanoparticles has been established. Reported results allow one to control and reliably predict the low-frequency and high-frequency behavior of the nanoparticle systems under investigation. The elaborated conclusions initiate a discussion on new functional possibilities for the development of the nanomaterials with improved and controllable magnetic parameters, which are promising for various technical and medical applications.