The first observation of 4d ferromagnetism in two-dimensional systems is reported. Using Auger electron spectroscopy, we find that the initial growth of Ru on a C(0001) substrate is lateral until a homogeneous monolayer film is formed. The magnetic properties of the films are studied using spin polarized secondary electron spectroscopy. For one monolayer Ru on C(OOOl), below a surface Curie temperature of approximately 250 K, nonzero in-plane spin polarization is observed and found to saturate in an applied field of a few tenths of an Oe. The results are discussed in the light of theoretical predictions.PACS numbers: 75.70. Ak, 75.30.Pd, 75.50.Cc, 79.20.Hx For the vast majority of elements, magnetism is found in isolated atoms, as shown by Hund's rules. In solids, however, the existence of spontaneous, long-range ferromagnetic order is restricted to only a few 3d-transition (Fe, Co, and Ni) and 4/ -rare-earth metals (Gd, Tb, Dy, Ho, Er, and Tm). Electronic structure calculations using state-of-the-art methods now reveal the exciting perspective that more elements might be forced to conserve their atomic magnetism, if properly synthesized at the nanometer scale.One way to achieve this goal and retain magnetic moments is to grow a metal, which is paramagnetic in its bulk form, epitaxially on an adequate nonmagnetic substrate. Ferromagnetic order in such ultrathin films may be induced by the reduced coordination number and hence reduced interatomic hybridization, band-structure effects due to the restriction to two dimensions, and, compared to the bulk paramagnetic solid, an increased lattice constant imposed by pseudomorphic film growth. An alternate way to preserve magnetic moments is to form small clusters which could be magnetic due to the reduced coordination and high symmetry. This leads to degenerate electronic states, which is an important condition for magnetism.So far, theoretical work has focused on the study of 4d-transition metals. It is found that the elements at the very end of the 4d series are likely candidates to exhibit magnetism [1][2][3][4][5][6]. For small clusters, this prediction recently was confirmed by Cox, Louderbaek, and Bloomfield [7], who found that small Rh clusters consisting of a few tens of atoms show magnetic ordering of the 4d electrons; the clusters are superparamagnetic with large magnetic moments. As to thin films, calculations were performed for ultrathin films deposited on the noble metals Ag and Au [l-5], which interact only weakly with the deposited atoms due to the large energy separation of the d bands. In addition, the larger lattice constant of Ag and Au would, compared to the bulk lattice constant of these 4d metals, increase the lattice constant in the films in the case of a pseudomorphic growth. All authors come to the 0031-9007/95 /74(17)/3467(4)$06.00 conclusion that both Ru and Rh monolayers on Ag(001) or Au(001) possess a ferromagnetic ground state.Subsequent experiments have been done for Rh on Ag(001) as well as Rh and Pd on Au(001), but failed to find any...

Total target currents for grazing scattering of keV protons from a crystal target are used to investigate the structure of surfaces and ultrathin films. This current shows pronounced maxima whenever the azimuthal incidence angle coincides with close-packed rows of atoms in the surface and subsurface layers. The real-space method is applied to study monolayer and bilayer films of Mn and of CoMn epitaxially grown on a Cu(001) surface.

We present a combined theoretical and experimental study of island nucleation and growth in the deposition of Co on Cu(001) -a prototype for understanding heteroepitaxial growth involving intermixing. Experimentally, ion scattering is employed. Using density-functional theory, we obtain energy barriers for the various elementary processes and incorporate these into a kinetic Monte Carlo program to simulate the heteroepitaxial growth. Both the simulations and the experiments show a unique N-shape dependence of the island density on temperature that stems from the interplay and competition of the different processes involved. DOI: 10.1103/PhysRevLett.90.076101 PACS numbers: 68.55.-a, 61.43.Hv, 68.35.Fx, 82.40.Bj Heteroepitaxial metallic structures, such as Co=Cu multilayers represent a new material that has high potential for the development of magnetoelectronic devices. In order to control the interfacial properties it is important to achieve a quantitative understanding of the morphology that develops during growth and its dependence on the growth conditions. A standard model for the initial stages of growth is given by nucleation theory [1], where the island density n x is expressed in terms of the deposition rate F, the adatom hopping rate D D 0 exp ÿE d =k B T , and the binding energy E b of the critical nucleus of size i,The linear dependence of lnn x on 1=T is widely used to deduce quantities such as activation barriers from islanddensity measurements, when adatoms form islands on top of the substrate [2]. However, in heteroepitaxial systems, deposited atoms may incorporate into the substrate displacing substrate atoms into the growing layer [3][4][5][6][7][8][9]. The effect of site exchange is not considered in Eq. (1). A prototypical system where intermixing takes place is Co on Cu(001). A broad [5,6] and bimodal [6] island-size distribution was observed in submonolayer growth studies using scanning-tunnelling microscopy (STM) -in contrast to a Poisson-like distribution anticipated in standard nucleation theory [1]. In addition Nouvertné et al. reported that the island density at 415 K is slightly higher than at 295 K [6], which is at variance with the predictions of Eq. (1). The island composition was found to depend on the growth conditions and to vary from mostly Co to mostly Cu. Moreover, a correlation has been observed between island composition and island size [5,6].From a fundamental standpoint, it is important to extend nucleation theories to account for intermixing. However, to date, only a few studies have attempted this [4,10 -13]. Chambliss and Johnson proposed that substitutional Fe atoms constitute stable nuclei for the growth of Fe on Cu(001) [4]. By accounting for monomer stability [i 0 in Eq. (1)] at substitutional Fe pinning sites, they found that the island density is independent of F=D. Meyer and Behm assumed irreversible pinning of adatoms at substitutional nucleation centers and found that the island density goes through a minimum with increasing temperature -consistent with that...

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