Quantum Confinement and Surface Effects on the Itinerant Ferromagnetism in Ni and Ni–Fe Nanowire Arrays: An Ab Initio Study

• Published in: physica status solidi (b) 2018-07, Vol.255 (7), p.n/a
• Main Authors: Ziti, Ikram, Britel, Mohammed Réda, Bouajaj, Adel, Wang, Chumin
• Format: Article
• Language: English
• Subjects: density functional theory; magnetic moments; nickel nanowires
• ISSN: 0370-1972; 1521-3951
• DOI: 10.1002/pssb.201700618

Coordination number reduction of surface atoms and spatial confinement of itinerant electrons are decisive factors in the nano‐ferromagnetism. Impacts of these factors on the ferromagnetic moments of Ni and Ni–Fe nanowire (NW) arrays are quantified by means of the density functional theory through both atomic‐orbital and plane‐wave approaches. A systematic study of the wire diameter, interwire distance and chemical composition on the magnetic properties were carried out in eight thin nanowires to investigate the limiting cases of confinement and surface effects. The results reveal a growth of the magnetic moment when the wire diameter diminishes, due to the decrease of average coordination number which reduces the 3d electronic band width and then a larger spin population contrast. This fact is consistent with experimental data obtained from Ni nanoparticles and NWs. Moreover, we found a critical interwire distance, which is the minimum separation that maintains the individual NW magnetic moment. Finally, both local and global magnetic moments of Ni–Fe NWs obtained from the ab initio calculations are compared with experimental ones and a good consistency is observed. Atomic‐orbital and plane‐wave density functional theory (DFT) approaches reveal threshold smearing and cutoff energies for accurate magnetic moment (µ) calculations, the former being more efficient. A significant increase of µ by reducing the diameter of the studied Ni and Ni–Fe nanowires is originated from the confinement and coordination number diminution at the surface. The finding of a critical interwire distance could be useful for the design of high‐density recording devices.