Magnetic properties of NixCo1-x nanoparticles in carbon nanotubes

X-ray diffraction analysis, nuclear magnetic resonance, and low-temperature magnetic measurements were used to study the structure and magnetic parameters of nanoparticles Co1-x Ni-x (x = 0-100 at. %) located inside carbon nanotubes. It has been established that the behavior of the exchange constant versus alloy composition A (x) is nonmonotonic. This fact is unexpectable from the thermodynamic viewpoint and primary X-ray diffraction analysis, which show that only an fcc structure is characteristic of all Co1-xNix particles. An analysis of structure defects using X-ray diffraction and NMR spectra explains the observed anomalies of magnetic properties as a result of the highly defect structure of ferromagnetic Co nanoparticles, which are formed as close-packed fcc structures with numerous stacking faults (layers of an hcp structure).