Magnetism In Nickel And Iron Nanomaterials By Ab Initio And Micromagnetic Calculations

With significant attention focused on nanoscience and nanotechnology in recentyears, nanomaterials have been propelled to the forefront by researchers from bothacademia and industry. The characteristic magnetic lengths are in the nanometer range,and novel magnetic phenomena in nanomaterials emerge. Therefore, the research intothenanomaterialsofferromagneticmetalssuchasnickelandironisofgreatimportancenot only in industrial applications, but also in fundamental theoretical physics.Ab initio methods and micromagnetics are applied to observe the spontaneousatomic magnetism and the macroscopic magnetic parameters, respectively. The mag-netism of nanosturcture is an interdisciplinary field, and the combinational utilizationof the two mainstream frameworks could lead a new direction to the nanomagnetismresearch.Calculations of spontaneous magnetism in HCP nickel nanowires by ab initomethods reveal the surface-enhanced ferromagnetism in the nanowires. Except for thesingle-layered one, all other nickel nanowires are core-shell structured. Core atoms innanowires have indentical magnetic moments to those in bulk HCP nickel metal, whilethe surface atoms behave stronger ferromagnetism. Despite the fact that the HCP struc-ture is metastable in bulk nickel, the ab inito results confirm the HCP nickel nanowiresin [0001] axial direction are energetical preferred to FCC nanowires in [111] axial di-rection when the diameters are small enough.Magnetism of icosahedral iron nanoparticle has been investigated by both ab initoand micromagnetic methods. Ab inito results reveal the highly structrual sensitiveatomic spontaneous ferromagnetism in iron icosahedrons. The symmetry of icosa-hedron affects the atomic magnetic moments and the electronic structures. But mostatoms still behave magnetism in range of FCC-strucured iron except the center atom.The micromagnetic results indicate that the high symmetry in icosahedrons causes thesoft magnetic properties in the hystersis loops. These interesting results suggest usual magnetic properties exist in the highly symmetric nanoparticles.