Magnetization dynamics in a highly nonlinear antiferromagnetic Josephson-like spintronic oscillator under the action of DC and AC signals is studied theoretically and numerically, and the regime of the oscillator synchronization to an external AC signal has been found and investigated. We revealed that the synchronization bandwidth of the oscillator substantially depends not only on the external force amplitude (which is typical), but also on the oscillator nonlinearity. This behavior arises from the highly nonlinear nature of the considered system. Our theoretical and numerical analyses show that the generation frequency of the oscillator depends on the applied electric DC current in a nonlinear way. Thus, the correct choice of the working point characterized by some particular value of the nonlinearity coefficient is important for the considered system to work properly, and it can be used for maximizing the oscillator synchronization bandwidth. Obtained results are important for the further development of antiferromagnetic terahertz-frequency spintronic oscillators and their applications. The developed formalism and numerical simulations can also be used for the description of strongly nonlinear non-isochronous oscillators of any nature.
The paper presents the results of investigation of structural and morphological peculiarities and transport properties of single-walled carbon nanotubes modified by cobalt-containing complexes. A scheme that allows simultaneously to clean the source nanocarbon material from the catalyst impurities and particles of disordered carbon, to separate single-walled tubes bunches into individual tubes, to cut the tubes along to defects and to modify tubes surface by cobalt-containing complexes is proposed. Using the thermomagnetometric method, it was found that attached to the surface of the carbon nanotubes cobalt is in the form of cations in the complicated complexes. When heating modified carbon nanotubes the complicated complexes are destroyed, and cobalt nanoparticles are formed. It is revealed that for bulk specimens of source single-walled carbon nanotubes the main mechanism of conductivity is the hopping conductivity with the variable hopping length for 3D system. Such conduction mechanism is typical of disordered graphite materials, as well as of mats and binders of single-walled carbon nanotubes. It is shown that modification of single-walled carbon nanotubes by cobalt-containing complexes results in a change in the character of the conductivity for bulk specimens of single-walled carbon nanotubes. For bulk specimens of modified singlewalled carbon nanotubes, conductivity is described in terms of power temperature law that is typical of individual single-walled carbon nanotubes. It is shown that such a change in the conduction mechanism during surface modification is associated with the creation of a small negative charge on the surface of nanotubes during the modification.
In the work, a series of theoretical calculations were carried out to analyze the possibility of the process of explosive crystallization during laser treatment of binary amorphous alloys of the Fe-Zr system. The calculations were carried out within the framework of the modified theory of homogeneous crystallization for binary alloys, which takes into account the work associated with the concentration fluctuation. Calculation of the characteristics of the crystallization process was performed for two modes: slow heating at a speed of 0.16 K/s and an instant laser pulse, while it was considered that the amorphous tape was heated by a laser beam to a certain temperature within 10-6 seconds. The integral curve of the temperature dependence of the volume part of the crystalline phase during slow isothermal annealings is characterized by the presence of a «shelf», which indicates the twostage crystallization process. The temperature range of crystallization at slow heating (0.16 K/s) is 90 K. We analyze the peculiarities of the crystallization process of amorphous alloys under the influence of laser treatment. The high heating rates, achieved by the laser treatment of amorphous alloys, create a number of differences in the course of crystallization processes compared with crystallization during slow isothermal annealings. According to the calculations, impulse heating to temperatures below 550 K does not cause crystallization. After 551 K, there are significant changes in the crystallization kinetics. At 552 K, the crystalline phase part has reached the value of 8 %. In the interval from 552 K to 553 K, there is a sharp jump in the value of the crystal phase proportion from 8 % to 99 %, that is a complete crystallization of the amorphous alloy occurs. The calculations carried out have shown that explosive crystallization may occur during the pulsed laser annealing of binary amorphous alloys of the Fe-Zr system. The temperature at which explosive crystallization is possible due to the laser pulse was less than 60 K for the temperature of the beginning of intensive crystallization at slow heating.
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