Structural and magnetic properties of large cobalt clusters

Abstract

We use a real-space implementation of pseudopotentials within the density-functional theory to investigate the structural and magnetic properties of cobalt clusters with up to 365 atoms. We find from structural optimization that hexagonal close-packed (hcp) and icosahedral clusters are lower in energy than body-centered cubic (bcc) and face-centered cubic (fcc) ones. We find the calculated magnetic moments generally decrease as a function of increasing cluster size. For clusters of several hundred atoms the bulk limit becomes apparent. However, the decrease is not monotonic. It depends on the details of the interior structure of the cluster and the corresponding surface geometry. By analyzing the detailed evolution of the local magnetic moment, we find the spin moment is bulk-like in the cluster interior and increases in the vicinity of the surface and can be correlated with coordination. The calculated behavior accounts for the observed variations in the measured moments.

Fe–Co magnetic nanoclusters by density functional theory calculations

“…In particular, the magnetic moment (MM) of Fe clusters with less than 100 atoms is around 3 μB much higher than the corresponding 2.2 μB bulk value while it decays as a function of clusters' size towards the bulk values [1][2][3][4][5]. Similar behaviour was also found by density functional theory (DFT) calculations when mixing Fe with a non-magnetic element like Cu in 13,55,147 and 309 magic numbered ICO clusters [6].…”

Size dependence of structural stability and magnetization of nickel clusters from real-space pseudopotentials

“…This results in an increase of the difference in electron population between majority (spin-up) and minority (spin-down) electrons and qualitatively accounts for an enhancement of the magnetic moments observed for these clusters within this size range. As shown in our previous work on Fe and Co clusters, [12][13][14] the structural and magnetic properties of 3d transition-metal clusters depend strongly on their geometrical structures such as local coordination, surface morphology, and nucleation site.…”

“…20,21 The exchange-correlation term is evaluated using the generalized gradient approximation (GGA) functional in the parameterized form of Perdew, Burke, and Ernzerhof, 22,23 which has been successfully applied to moderately correlated systems including transition-metal clusters. [12][13][14] The Kohn-Sham equation is solved self-consistently using the parsec code. [24][25][26][27] The wave functions and the potentials are sampled on an uniform grid in real space.…”

“…34 Moreover, parsec enjoys the benefit of massive parallelization, making it feasible to compute the electronic structures of magnetic clusters containing hundreds of atoms. 14…”

Binding modes of carboxylic acids on cobalt nanoparticles

“…Cobalt nanoparticles have been shown experimentally and theoretically to favour a non-crystalline icosahedral morphology for the smallest sizes, with large nanoparticles expected to adopt hcp-bulk geometry. [23][24][25] A variety of ligands have so far been tested to enhance biocompatibility, improve growth control, stabilise the particle dispersions, prevent agglomeration, provide functionality, and limit the surface reactions. By now it is known that metallic nanoparticles experience strong van der Waals and magnetic dipole interactions, hence only the surfactants which covalently bond to the metal can considerably promote their stability.…”