The thesis is devoted to the complex research of the structure, electrophysical, magneto - optical and magnetoresistive properties of nanosized film layered asymmetric structures, in which the effect of giant magnetoresistance is observed. The basis for the formation of such structures are ferromagnetic metals Fe, Ni, Co, as well as their alloys: FexNix and CoCr. Thin layers of Cu, Cr and Pt were used as a non-magnetic component. In addition, the effect of temperature influence on the structural - phase composition of Fe3O4, NiFe2O4 and CoFe2O4 ferrite nanoparticles, which can act as a basic magnetic component in structures such as magnetic nanoparticles / conductive matrix, in which, like in granular structures, giant magnetoresistance effect can be realized
Usual sampling techniques were used the for film systems, such as layer-by-layer and simultaneous deposition from two independent sources, followed by annealing to a temperature of 500 - 800 K. Transmission electron microscopy was used as a method to control the structure and change of the phase composition after annealing.
Multilayer film structures were obtained by layer-by-layer deposition from independent sources, followed by annealing to a temperature of 400 - 800 K. Nanoparticles of ferrites were obtained by chemical synthesis by reaction between acetylacetonate Fe, Ni and Co with 1,2 - hexadecanediol and oleic acid and oleilamino surfactant in phenyl ether. Several methods were used to apply the particles to the substrate, namely the dripping of a solution with nanoparticles on the substrate, the modified Langmuir-Blodget technique, and the spin-coating method. In addition to transmission microscopy for nanoparticles, raster electron microscopy and atomic force microscopy methods were additionally used to control the perfection of the formed layers.
Emphasis was placed on the analysis of changes in the magnetic characteristics of film systems, such as coercive force Bc, residual magnetization HR, saturation magnetization Hs and Kerr angle, which in this case are indicators of the transition from one phase to another.
It is theoretically shown that for asymmetric structures the inversion (change of sign) of the GMR effect is possible provided that the spin asymmetry in electron scattering is opposite in adjacent ferromagnetic layers.
Asymmetric systems also include structures in which, as one of the magnetic layers, an alloy can act. In our case it was an alloy based on permalloy FeNi and Cu. The study of the phase composition of films by electron diffraction showed that in all as-deposited and annealed at 700 K FeNi films with a thickness d = 20 - 100 nm, as well as in massive samples of the corresponding composition, fixed FCC - NiFe phase with lattice parameter a = 0.360 - 0.361 nm.
The last stage was the study of structural - phase changes during heat treatment of Fe3O4, NiFe2O4 and CoFe2O4 nanoparticles. Heat treatment is necessary due to the fact that the original nanoparticles are very small (3 - 10 nm) and are in a superparamagnetic state. That is why we need to achieve the effect of increasing the particle size, while maintaining their phase composition. It was shown that in the temperature range 300 - 600 K the phase state of the particles with a slight increase in their size is preserved. A further increase in the annealing temperature to 800 K leads to a significant decrease in the intensity of some lines, which indicates the beginning of the phase transition. After 800 K, the decomposition of oxides begins and a large number of auxiliary phases are formed. At a temperature of 1100 K, the oxides finally decompose and the Fe and Ni phases stabilize. In fact, nanoparticles remain in the initial phase state only up to 800 K, after which their decay begins. The increase in particle size occurs due to their coagulation with sedimentary particles. However, this increase did not lead to the desired effect, and their total magnetic moment was insufficient to obtain a response in the study of magnetoresistive properties.
From the data analysis it becomes clear that the most effective method of obtaining homogeneous layers is the Langmuir-Blodget technique.. The disadvantage is the incomplete filling of the surface. Separately, we highlight the method of spin - coating. Due to its relative simplicity, depending on the parameters used (NP concentration and rotation speed), it is possible to obtain structures of completely different types, with different distribution on the substrate. However, we were not able to obtain a homogeneous layer of nanoparticles, because, even at low concentrations of NP in solution, the formation of clusters of different sizes (clusters) was observed.
