Keywords: nanostructures, electron–electron interactions, band narrowing, nanomaterials, nanotechnology, Coulomb correlations, monatomic nanowires, magnetism, nanomagnetism, extended Hubbard model, ferromagnetism, spin channels, spintronic devices
Effect of Coulomb correlations on one–dimensional monatomic nanowire
The experimental realisation of one–dimensional (1D) monatomic chains of transition elements has opened a new route to study the magnetism in nanostructures in the field of condensed matter physics. We studied a so–called extended Hubbard model which includes all the off–diagonal matrix elements of Coulomb interactions, to explain the phenomenon of ferromagnetism in 1D monatomic chain of itinerant ferromagnets like Fe, Co and Ni. We have used the Green's function equation of motion approach to get energy eigenvalue of quasi–particle. Within the mean field approximation, among the off–diagonal matrix elements, the effect of correlated hopping is very crucial, because the magnitude is larger than exchange interaction. Therefore, in 1D itinerant ferromagnets, the ferromagnetism is driven by combined effect of band splitting and band narrowing/broadening. As a result of it, for the systems with less than half filled band, the up spin band gets broadened and down spin band narrowed down and vice versa for more than half filled band systems. From available Density Functional Theory (DFT) results it can be seen that up spin channel is present for conduction near Fermi level in the systems with less than half filled band and vice versa for more than half filled band systems. This effect is more pronounced in the presence of external magnetic field. Presence of one spin channel is one of the requirements for spintronic devices. The obtained results are in good agreement with existing DFT results.