Ab Initio Studies On Magnetic Properties Of Metallic Clusters

Metallic clusters own many unique physical and chemical properties. Especially their outstanding magnetic performances have attracted a lot of attentions from people who want to further shrink the size of data storage. Density functional theory has provided powerful tools for studying magnetic characters of metallic clusters. In this paper, we have systematically investigated the magnetic properties of free zero-dimensional clusters（free Pd-Co alloy clusters） and one-dimensional clusters（3d metal monoatomic chains） supported by Cu₂N surface with first-principles calculations. Results turn out that the magnetic properties of clusters can be tailored by chemical adsorption or exchange interaction. This thesis is arranged as following two parts:1. Research on magnetic properties of Pd-Co alloy clustersIn the ground structures of free alloy clusters（Pd_n Co, n = 1-4）, Co atom tend to occupy with the most coordinate number of Pd atoms. Doping a Co atom into pure Pd clusters enhances the total magnetic moment（from 2 μ_B to 3 μ_B）, but slightly reduces the moment of each atom. This is because that the electrons shared by Pd and Co atoms partly fill the minority orbitals of d shells in each atom. When n = 1, the cluster’s magnetic moment decrease as one H atom adsorbed at first, then increase as another H atom adsorbed. Whereas when n = 2, 3, 4, the moments will increase at first then decrease. This tendency can be inferred by analyzing the cluster’s density of states（DOS） around Fermi level.2. Research on magnetic properties of antiferromagnetic monatomic chainsOn Cu₂N surface, antiferromagnetic（AFM） monatomic chains can be obtained artificially by using scanning tunneling microscope（STM） tip. In this part of work, we demonstrate that two indistinguishable Néel states of an antiferromagnetic chain can be tailored into a preferred state by the exchange interaction with a magnetic STM tip. The magnitude and direction of the anisotropy for antiferromagnetic chains can also be tuned by exchange coupling upon varying the tip–chain separation.