Ligand mediated evolution of size dependent magnetism in cobalt nanoclusters

Abstract

We use density functional theory to model the impact of a ligand shell on the magnetic properties of Co_N (15 ≤ N ≤ 55) nanoclusters. We study three different ligand shells on each nanocluster core size, each known to have different electronic interactions with the surface: pure Cl ligand shells (X-type), pure PH₃ ligand shells (L-type), and two component ligand shells with mixtures of Cl and PH₃ ligands. The simulations show that the identity, arrangement, and total coverage of the ligand shell controls the distribution of local magnetic moments across the Co_N core. On the surface of an unpassivated Co_N nanocluster, the Co–Co coordination number (CN) is known to determine the local magnetic moments. Upon the introduction of a ligand, the Co–Co CN remains important, however the nature of the metal–ligand bond changes the extent to which increasing Co–Co CN quenches magnetism. Further, we identify an additional and significant long-range impact on local magnetic moments (LMM) from the PH₃ ligand shells. Thus, we establish important design principles of magnetic nanoclusters, where ligand shell chemistry mediates the distribution of LMMs across a Co_NL_M nanocluster, allowing a route to rational design of specific magnetic properties.