Fe clusters on Ni and Cu: size and shape dependence of the spin moment (original) (raw)
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Spin and orbital moments of Fe clusters supported on Ni(001
Journal of Physics-condensed Matter, 2008
The spin and orbital moments for small Fe clusters deposited on a Ni(001) surface have been calculated by means of an ab initio method. We find enhanced spin and orbital moments compared to what is found in bulk Fe. Our obtained spin moments are in good agreement with previous theoretical studies on similar systems. Comparing our results with a recent x-ray magnetic circular dichroism study [J. T. Lau et al 2002 Phys. Rev. Lett. 89 057201], we find that the calculated orbital moments are much lower than the experimentally found. Reasons for this discrepancy are discussed.
Structure and magnetic properties of small Fe clusters supported on the Ni(001) surface
Physical Review B, 2005
Using the modified embedded atom model in conjunction with a self-consistent tight-binding method, we calculated the structures and magnetic properties of small Fe n clusters ͑n =2-9͒ supported on the Ni͑001͒ surface. The structures are predicted to be two-dimensional islands, and the average spin magnetic moment per d hole is found hardly to vary with n. This latter finding contrasts with conclusions recently drawn on the basis of x-ray magnetic circular dichroism results. The magnetic moments of the individual Fe atoms in each cluster tended to increase with decreasing coordination number, and noncollinear tight-binding calculations showed all systems to be ferromagnetic. Cluster magnetism was hardly affected by Fe-Ni hybridization.
The spin and orbital contributions to the total magnetic moments of free Fe, Co, and Ni clusters
The Journal of chemical physics, 2015
We present size dependent spin and orbital magnetic moments of cobalt (Con (+), 8 ≤ n ≤ 22), iron (Fen (+), 7 ≤ n ≤ 17), and nickel cluster (Nin (+), 7 ≤ n ≤ 17) cations as obtained by X-ray magnetic circular dichroism (XMCD) spectroscopy of isolated clusters in the gas phase. The spin and orbital magnetic moments range between the corresponding atomic and bulk values in all three cases. We compare our findings to previous XMCD data, Stern-Gerlach data, and computational results. We discuss the application of scaling laws to the size dependent evolution of the spin and orbital magnetic moments per atom in the clusters. We find a spin scaling law "per cluster diameter," ∼n(-1/3), that interpolates between known atomic and bulk values. In remarkable contrast, the orbital moments do likewise only if the atomic asymptote is exempt. A concept of "primary" and "secondary" (induced) orbital moments is invoked for interpretation.
Physical Review B, 2007
The magnetic structures of small clusters of Fe, Mn, and Cr supported on a Cu(111) surface have been studied with non-collinear first principles theory. Different geometries such as triangles, pyramids and wires are considered and the cluster sizes have been varied between two to ten atoms. The calculations have been performed using a real space linear muffin-tin orbital method (RS-LMTO-ASA). The Fe clusters are found to order ferromagnetically regardless of the cluster geometry. For Mn and Cr clusters, antiferromagnetic exchange interactions between nearest-neighbours are found to cause collinear antiferromagnetic ordering when the geometry allows it. If the antiferromagnetism is frustrated by the cluster geometry non-collinear ordering is found. A comparison between the calculated structures and ground states obtained from simplified Heisenberg Hamiltonians show that the exchange interaction varies for different atoms in the clusters as a result of the different local structure.
Magnetic moment and local moment alignment in anionic and/or oxidized Fe clusters
2010
First principles studies on the ground state structure, binding energy, spin multiplicity, and the noncollinearity of local spin moments in Fe n and Fe n − clusters and their oxides, viz., Fe n O 2 and Fe n O 2 − have been carried out within a density functional formalism. The ground states of Fe n and Fe n − clusters have collinear spins with a magnetic moment of around 3.0 B per atom. The O 2 molecule is found to be dissociatively absorbed and its most significant effect on spin occurs in Fe 2 , where Fe 2 O 2 and Fe 2 O 2 − show antiferromagnetic and noncollinear spin arrangements, respectively. The calculated adiabatic electron affinity and the vertical transitions from the anion to the neutral species are found to be in good agreement with the available negative ion photodetachment spectra, providing support to the calculated ground states including the noncollinear ones.
The Journal of Chemical Physics, 2005
We report ab initio calculations of the structures, binding energies, and total spins of the clusters Ni(13), Ni(19), Ni(23), Ni(26), Ni(12)Fe, Ni(11)Fe(2), Ni(18)Fe, Ni(17)Fe(2), Ni(22)Fe, Ni(20)Fe(3), and Ni(25)Fe using a density-functional method that employs linear combination of atomic orbitals as basis sets, nonlocal norm-conserving pseudopotentials, and the generalized gradient approximation for exchange and correlation. Our results show that the Fe-doped Ni clusters, which have icosahedral or polyicosahedral ground-state structures similar to those of the corresponding pure Ni clusters, are most stable with the Fe atoms occupying internal positions, as has also been inferred from experimental results on the adsorption of molecular nitrogen on the cluster surfaces. We also rule out the possibility that the experimentally observed difference between the (nonpolyicosahedral) configurations of N(2)-saturated Ni(26) and N(2)-saturated Ni(25)Fe be due to the influence of the Fe atom on the energy of the underlying metal cluster.
Magnetic moments of Ni clusters
Physical Review B, 1998
The geometries and electronic structures for Cu X Ni 8−X (X = 1-8) clusters have been elucidated using density functional theory methods. These clusters have been demonstrated to be eight superatomic electron species, with a substantial HOMO-LUMO gap and closed 1S and 1P subshells. Through sequential replacement of copper atoms for nickel in these clusters it has been shown that the magnetic moment of bimetallic clusters can be controllably altered, with the nickel atoms localising spin density in their 3d orbitals.
Magnetic properties of clusters of transition metal atoms
Europhysics Letters (EPL), 1996
Using a newly proposed calculational scheme that combines the Hubbard approximation with the tight-binding molecular-dynamics method, we obtain the magnetic moments of Fen and Nin clusters with cluster size up to n = 55 in a systematic way. Our results indicate that the average magnetic moment per atom is significantly higher in the cluster than in the bulk, in agreement with recent experimental data for Fe and Ni clusters. Furthermore, it is found that magnetic effects stabilize the clusters in geometries that were found to be completely unstable when magnetism is ignored. In general, magnetic effects drive Fe (and to a lesser extent Ni) clusters into geometries of higher symmetry than that of the corresponding singlet states.
Magnetic structure of Fe, Mn, and Cr clusters supported on Cu (111)
The magnetic structures of small clusters of Fe, Mn, and Cr supported on a Cu(111) surface have been studied with non-collinear first principles theory. Different geometries such as triangles, pyramids and wires are considered and the cluster sizes have been varied between two to ten atoms. The calculations have been performed using a real space linear muffin-tin orbital method (RS-LMTO-ASA). The Fe clusters are found to order ferromagnetically regardless of the cluster geometry. For Mn and Cr clusters, antiferromagnetic exchange interactions between nearest-neighbours are found to cause collinear antiferromagnetic ordering when the geometry allows it. If the antiferromagnetism is frustrated by the cluster geometry non-collinear ordering is found. A comparison between the calculated structures and ground states obtained from simplified Heisenberg Hamiltonians show that the exchange interaction varies for different atoms in the clusters as a result of the different local structure.
Physical Review B, 2012
We present a detailed theoretical investigation on the magnetic properties of small single-layered Fe, Co and Ni clusters deposited on Ir(111), Pt(111) and Au(111). For this a fully relativistic abinitio scheme based on density functional theory has been used. We analyse the element, size and geometry specific variations of the atomic magnetic moments and their mutual exchange interactions as well as the magnetic anisotropy energy in these systems. Our results show that the atomic spin magnetic moments in the Fe and Co clusters decrease almost linearly with coordination on all three substrates, while the corresponding orbital magnetic moments appear to be much more sensitive to the local atomic environment. The isotropic exchange interaction among the cluster atoms is always very strong for Fe and Co exceeding the values for bulk bcc Fe and hcp Co, whereas the anisotropic Dzyaloshinski-Moriya interaction is in general one or two orders of magnitude smaller when compared to the isotropic one. For the magnetic properties of Ni clusters the magnetic properties can show quite a different behaviour and we find in this case a strong tendency towards noncollinear magnetism.