Magnetism and structure on the atomic scale: Small cobalt clusters in Cu(001)

Abstract

The interplay between structure and magnetic properties of small cobalt clusters embedded in a Cu(001) surface is studied performing ab initio and tight-binding calculations in a fully relaxed geometry. We reveal that, despite the small macroscopic mismatch between Co and Cu, the strain relaxations at the interface have a profound effect on the structure of the clusters and the substrate. The physical mechanism responsible for the strain relaxations in embedded clusters is related to the size-dependent mesoscopic mismatch which has been recently introduced to understand homo-and heteroepitaxial growth at the mesoscale [O. V. Lysenko et al., Phys. Rev. Lett. 89, 126102 (2002)]. We show that the atomic relaxations strongly reduce the magnetic anisotropy energy (MAE) and the orbital magnetic moments of embedded clusters. The largest MAE of about 1.8 meV is found for a single Co atom in the Cu(001) surface. A strong enhancement of the spin magnetic moments in embedded clusters as compared to a single atom of Co incorporated in the Cu(001) surface is found. Magnetic properties of embedded and supported clusters are compared. While in supported clusters the MAE is strongly enhanced at the edge atoms, the immersion of the cluster into the surface and atomic relaxations make the distribution of the local MAE contributions and orbital-moment values almost homogeneous.

Magnetic properties of small Pt-capped Fe, Co, and Ni clusters: A density functional theory study

“…Theoretically, there have been several studies on magnetic anisotropy for supported clusters [27,28,29,30,31,32,33], whereas studies on small free clusters are still limited [34,35,36,37,38]. The motivation for the present study is that icosahedral clusters for M 13 are known to be very stable, [6,12,39] and the alloying of 3d transition metals with Pt results in large magnetic anisotropy as well as orbital moment.…”

Effect of mesoscopic misfit on growth, morphology, electronic properties and magnetism of nanostructures at metallic surfaces

“…While in supported clusters the MAE is strongly enhanced at the edge atoms, the immersion of the cluster into the surface and atomic relaxations make the distribution of the local MAE contributions and orbital-moment values almost homogeneous. [144] 4. Experimental confirmation of mesoscopic mismatch I: surface x-ray diffraction…”

Structure and magnetic properties of Co chains on a stepped Cu surface

“…To make the extensive calculations feasible, only the changes introduced by the geometry relaxation of the Co atoms and their nearest neighbors are taken into account. It has been demonstrated in our previous studies [38,44] that moderate perturbation of more distant Cu atom can be safely neglected. The parameters of a semi-empirical TB Hamiltonian are fitted to reproduce closely the ab initio KKR results for ideal chains at the step (atomically resolved local density of states (LDOS) and magnetic moments).…”

“…The local densities of states (LDOS) and electronic properties of interest are calculated with the help of the recursion method technique (continued fraction with large number of levels) [46,47]. Actually, the method is essentially the same as in our previous investigations [38,44]. In order to avoid too sharp peaks near E F we have changed the small ddδ parameter of Co [48] to fulfill the canonical prescription [49] ddσ :ddδ = 6:1.…”