Interaction of electromagnetic radiation in the 20–200 GHz frequency range with arrays of carbon nanotubes with ferromagnetic nanoparticles

The interaction of electromagnetic radiation with a magnetic nanocomposite based on carbon nanotubes (CNT) is considered within the model of distributed random nanoparticles with a core–shell morphology. The approach is based on a system composed of a CNT conducting resistive matrix, ferromagnetic inductive nanoparticles and the capacitive interface between the CNT matrix and the nanoparticles, which form resonance resistive–inductive–capacitive circuits. It is shown that the influence of the resonant circuits leads to the emergence of specific resonances, namely peaks and valleys in the frequency dependence of the permeability of the nanocomposite, and in the frequency dependence of the reflection and transmission of electromagnetic radiation

Anisotropy of Assemblies of Densely Packed Co-Alloy Nanoparticles Embedded in Carbon Nanotubes

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.We report the magnetic properties of an array of binary CoFe, CoNi and CoPt nanoparticles (NPs) embedded inside vertically oriented carbon nanotubes (CNTs). Samples were synthesized by chemical vapor deposition activated by current discharge plasma and hot filament. Assemblies of Co-based catalytic NPs have been preliminary formed on SiO2/Si substrates by sputtering of ultrathin films followed by reduction in H2/NH3 mixture. As a result, each CNT contained only one ferromagnet top-located NP. Magnetic hysteresis loops for both parallel and perpendicular magnetic field orientations revealed anisotropy of magnetic properties. For all samples the easy axis of magnetization were oriented along the CNT axis. Using the obtained experimental data and the random anisotropy model, the magnetic parameters like the effective anisotropy constant, the contribution of dipole interaction, shape, magnetocrystalline and magnetoelastic anisotropy were estimated. It is shown that the latter contribution of anisotropy is decisive. From the obtained magnetoelasticity the stresses in the CNT array with studied NPs were determined. Finally, the magnetization distribution in CoFe, CoNi and CoPt NPs was simulated considering the magnetoelastic contribution

Superconducting critical temperature and softening of the phonon spectrum in ultrathin nb- and nbn/graphene hybrids

Superconductivity is studied in hybrids consisting of ultrathin superconducting film/few layer graphene. Two different superconductors are used for this purpose, Nb and NbN. An increase in the superconducting critical temperature Tc is observed when graphene is put into contact with Nb. The largest increase is obtained for the thinnest Nb layer, which has a Tc 8% larger with respect to the single Nb film. In the case of NbN the effect is not as pronounced. Experimental data are discussed by considering the possible modification of the phonon spectrum in the superconductor due to the presence of the graphene. Within an elementary one-dimensional model based on elastic coupling between nearest-neighbor atoms, we demonstrate that the phonon spectrum in the superconductor is modified at low energies with the subsequent enhancement of the effective electron–phonon coupling constant. While the strong oscillating nature of the electron–phonon interaction, α2(ω), in NbN could lead to the insensitivity of Tc on the low-energy phonons generated by the graphene, the almost constant behavior of α2(ω) in Nb favors the increase of the superconducting critical temperature