Uniaxial anisotropy has been found in ultrathin cobalt films grown on a Cu(l 1 13) surface. Our studies using scanning electron microscopy with polarization analysis clearly show that the easy axis of magnetization is parallel to the direction of the step edges of the Cu(l 113) substrate. In spite of the different anisotropy behavior, the domain structures in Co/Cu(00l) and Co/Cu(l 1 13) are similar, which indicates that the domain pattern in ultrathin films is little affected by the anisotropy. PACS numbers: 75.30.Gw, 75.60.Ch, 75.70.Ak Recent scientific and technical advances in surface science and thin-film preparation methods have opened up a new class of research activities, i.e., the investigation of new artificially grown materials. One fascinating aspect of such studies is the ability to compare properties of the same material in different forms. Different crystal structures can be stabilized by the appropriate choice of substrates, phases that otherwise do not occur in nature such as bcc Co [1], fee Co [2], fee Fe [3], and bec Cu [4l.A further item of interest with these artificial materials concentrates on the exploitation of the transition from threeto two-dimensional crystals. For that purpose, the investigation of ultrathin films, i.e., films of a few monolayer thickness, has gained more and more importance in recent times. Apart from the general interest in studying dimensionality effects, there is a profound interest in understanding ultrathin films from the technological point of view, as novel devices continue to shrink in size.Investigations of magnetism in ultrathin films impressively demonstrate the variety of effects which can be found in ferromagnets of diminishing thickness. In many cases the effects manifest in the magnetic anisotropy of the films [5], For the interpretation and understanding of the magnetic properties it turns out that it is of great importance to distinguish the purely magnetic properties from those induced via magnetoelastic interactions by the film/substrate interface [6]. One approach to solve that problem is to study the ultrathin-film magnetism in a film system with a perfect and ideal substrate/film interface. The system Co/Cu(001) is well known from the literature to fulfill the above condition, and is well characterized concerning growth as well as magnetic properties [2,7-9]. The system exhibits layer-by-layer growth. The anisotropy behavior is determined by the film symmetry; no interface (i.e., magnetoelastic) effects altering these symmetry properties have been found for the cobalt films. Thus Co/Cu(001) is the ideal reference system for the investigations of substrate-induced magnetic film properties. These considerations let us use a slightly different template with a well-characterized and defined modification of the Cu(001) surface, i.e., the Cu(l 1 13). The main difference between Cu(00l) and Cu(l 1 13) is the reduced symmetry of the Cu(l 1 13) surface due to the existence of well-oriented steps. The influence of the symmetry on the magnetic properties o...
We present a combined study of the growth, structure, and related magnetic properties of Fe/W(001) using low-energy electron diffraction, scanning tunneling microscopy, the magneto-optic Kerr effect, and scanning electron microscopy with polarization analysis. Different growth regimes arise due to a competition between the stress-related elastic energy and diffusion barriers. By increasing the growth temperature, diffusion mechanisms may be switched on, activating more and more diffusion paths that lead to a reduction of the elastic energy stored in the growing films. This results in strong variations of the structure and morphology of the films. The influence of each structural and morphological phase of the Fe films on the magnetic properties can be observed and is interpreted within micromagnetic theory
In the highly strained system Fe/W(001) the formation of parallel dislocation bundles upon nucleation of fifth layer islands is used to locally break the fourfold symmetry. The uniaxial strain relief in the dislocation bundles introduces strong uniaxial in-plane magnetic anisotropies. By controlling the density of fifth layer islands local magnetic anisotropies are structured on the nanometer scale. As a result of this patterning of anisotropies, the magnetic properties of the films are drastically altered. As a function of the pattern size, the coercivity of the films can be varied in a controlled way over more than two orders of magnitude without changing the film thickness. For pattern sizes larger than the estimated domain wall width, MOKE and micromagnetic calculations indicate the break-up of the film into magnetic in-plane structures on the 100 nm scale.
We have investigated the magnetism of the bare and graphene-covered (111) surface of a Ni single crystal employing three different magnetic imaging techniques and ab initio calculations, covering length scales from the nanometer regime up to several millimeters. With low temperature spinpolarized scanning tunneling microscopy (SP-STM) we find domain walls with widths of 60 -90 nm, which can be moved by small perpendicular magnetic fields. Spin contrast is also achieved on the graphene-covered surface, which means that the electron density in the vacuum above graphene is substantially spin-polarized. In accordance with our ab initio calculations we find an enhanced atomic corrugation with respect to the bare surface, due to the presence of the carbon pz orbitals and as a result of the quenching of Ni surface states. The latter also leads to an inversion of spinpolarization with respect to the pristine surface. Room temperature Kerr microscopy shows a stripe like domain pattern with stripe widths of 3 -6 µm. Applying in-plane-fields, domain walls start to move at about 13 mT and a single domain state is achieved at 140 mT. Via scanning electron microscopy with polarization analysis (SEMPA) a second type of modulation within the stripes is found and identified as 330 nm wide V-lines. Qualitatively, the observed surface domain pattern originates from bulk domains and their quasi-domain branching is driven by stray field reduction.
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