Magnetic properties of FeCo nanoclusters on Cu(100):Ab initiocalculations

Abstract

We present ab initio calculations of the magnetic moments and magnetic anisotropy energies of small FeCo clusters of varying composition on top of a Cu͑100͒ substrate. Three different cluster layouts have been considered, namely, 2 ϫ 2, 3 ϫ 3, and crosslike pentamer clusters. The ratio of Co atoms with respect to the total number in a chosen cluster ͑"concentration"͒ was varied and all possible arrangements of the atomic species were taken into account. Calculations have been performed fully relativistic using the embeddedcluster technique in conjunction with the screened Korringa-Kohn-Rostoker method and the magnetocrystalline anisotropy energy ͑MAE͒ has been evaluated by means of the magnetic force theorem. A central result of the investigations is that the size of the magnetic moments of the individual Fe and Co atoms and their contributions to the anisotropy energy depend on the position they occupy in a particular cluster and on the type and the number of nearest neighbors. The MAE for the 2 ϫ 2 and 3 ϫ 3 clusters varies with respect to the concentration of Co atoms in the same manner as the corresponding monolayer case, whereas the pentamer clusters show a slightly different behavior. Furthermore, for the clusters with an easy axis along a direction in the surface plane, the MAE shows a significant angular dependence.

High magnetic moments and anisotropies forFexCo1−xmonolayers on Pt(111)

“…This is clearly seen comparing, for example, our results with similar ones for an FeCo monolayer on Cu͑100͒. 70 In this last case the MAE is found to have a linear dependence on the film composition.…”

Exchange coupling in transition‐metal nanoclusters on Cu(001) and Cu(111) surfaces

“…The spin moments in Fe clusters have been found to vary in a regular way, namely the moment of each Fe atom scales down linearly as a function of the number of Fe neighbours 8–10. This nice effect seems to be independent of the substrate, and persists also in FeCo clusters 11. On the other hand, in pure Co clusters the moment is practically saturated, while in Ni clusters the atomic moments do not seem to correlate with the coordination number.…”

Magnetic properties of single atoms of Fe and Co on Ir(111) and Pt(111)

“…This behavior, now quite wellknown to be characteristic for small magnetic clusters on top of metal substrates, [6], [4] is due to the lower coor- dination of the surface atoms which favors an incomplete quenching of orbital contributions. For both kinds of adatoms, Fe and Co, the magnetic moments are larger when deposited on a Pt substrate, a peculiar feature, which most likely is caused by the stronger polarization of Pt than that of an Ir substrate, see Fig.…”

“…If materials can be manufactured which exhibit sufficiently large anisotropies and thermal stabilities it may become possible to store one bit in a single grain [1]. Such storage devices will require magnetic structures of precise atomic arrangement, as -if in addition the lateral dimensions of grains are further reduced -the influence of the perimeter atoms becomes increasingly important [2,3] and, as is known, from previous studies the magnetic properties of each atom in a nanostructure are highly influenced by its local environment [1,2,3,4].Using Scanning Tunneling Microscopy structures can be precisely tailored and their magnetic properties determined. In recent Scanning Tunneling Spectroscopy experiments [3,5] it has become possible to measure not only the Lande g-factor of individual atoms but also their magnetic anisotropy.…”

“…If materials can be manufactured which exhibit sufficiently large anisotropies and thermal stabilities it may become possible to store one bit in a single grain [1]. Such storage devices will require magnetic structures of precise atomic arrangement, as -if in addition the lateral dimensions of grains are further reduced -the influence of the perimeter atoms becomes increasingly important [2,3] and, as is known, from previous studies the magnetic properties of each atom in a nanostructure are highly influenced by its local environment [1,2,3,4].…”