J. Giergiel

Stages of structural transformation in iron thin film growth on copper (100)

Abstract We report on an attempt for a complete qualitative investigation of γ → α phase transformation in iron films grown at room temperature on Cu(100). To this end we characterize the surface morphology across the full transformation range using a special scanning tunneling microscope that allows imaging one particular area of the sample as it undergoes the growth induced transformation. We report for the first time, that the system is unstable toward a structural rearrangement at coverages as low as 4.6 ML, that it develops a very characteristic network of surface features and we will describe these features and their evolution in detail. The structural transformation is initiated by formation of dislocation-like thin elongated ridges which later transform into a very complicated system of bcc precipitates. Several paths of these transformations are identified. Their multiplicity reflects the complexity of processes that drive this transformation. A brief description of driving forces, a possible transformation mechanism and a correlation with magnetic properties will be given.

Surface alloying and pinhole formation in ultra-thin FeCu(100) films

Abstract Relatively mild annealing sometimes produces unexpectedly large changes in surface composition of ultra-thin films. We report results of a scanning tunnelling microscopy study of such annealing in an Fe Cu (100) system. Copper appears in the surface region after a short 490 K anneal. We specifically exclude the possibility of bulk interdiffusion and conclude that this surface copper comes from the substrate through microscopic pinholes. Our primary finding is that the balance of surface free energies which strongly prefers Cu/Fe/Cu over Fe Cu is the main driving force for pinhole formation and copper segregation. Furthermore, we report a significant surface alloying in this otherwise almost immiscible system.

Epitaxial growth of Fe on Mo(110) studied by scanning tunneling microscopy

Scanning tunneling microscopy has been used to investigate the growth of Fe on Mo(110). Growth was carried out at room temperature with growth rates between 0.03 and 0.5 ML min’1. Initially, the first atomic layer is completed independently of the rate of evaporation. At low deposition rates the further growth proceeds in a multi-layer fashion whereas at higher rates the layer growth is partially preserved. Preferred growth along the [001] direction is observed in some cases. One-dimensional dislocation lines are observed in the second-layer islands. At higher coverage a two-dimensional dislocation network occurs which vanishes for thicker films. At a temperature of 600 K Fe on Mo(110) grows by a step flow mechanism in the first layer followed by the formation of wedge-shaped three-dimensional islands. A comparison with Fe grown on W(110) at a similar deposition rate is provided.

Annealing effect on morphology and magnetism of ultrathin films of Fe and Ni on Cu(100)

Abstract Scanning tunneling microscopy (STM) and the magneto-optical Kerr effect (MOKE) have been used to investigate the effects of annealing on the morphology and magnetism of Fe and Ni films on Cu(100). Relatively mild annealing (490 K) created pinholes in the Fe/Cu(100) films, opening channels for the surface diffusion of copper to the top of the film surface along the walls of the pinholes. The magnetization of the Fe films is strongly affected by annealing. Annealing smooths the surface of Ni/Cu(100) films significantly, but no interdiffusion was observed upon annealing below 500 K. For Ni films thicker than 7 ML, the magnetization remains perpendicular after annealing, with only a slight reduction in its amplitude.

On the Barkhausen volume in ultrathin magnetic films with perpendicular anisotropy

Abstract Magnetic aftereffect studies as well as in-situ domain observation are performed on γ-Fe/Cu(001) films, providing the Barkhausen volume values for these samples. On the basis of comparative STM studies we propose the structural origin of the Barkhausen volume to be related to the atomic terraces of the Cu(001) substrate.

Comparison of magnetism and morphology of ultrathin Fe films on Cu(100) and Cu3Au(100)

In order to obtain a deeper insight into the inter-relation of magnetism and morphology we compare the properties of Fe films on Cu(100) and Cu 3 Au(100) grown at different temperatures, using the magneto-optical Kerr effect and scanning tunnelling microscopy. In Fe films on Cu 3 Au(100) for both room- and low-temperature growth (RT and LT growth) neither an antiferromagnetic phase nor a good layer-by-layer growth, as found for RT growth in Fe/Cu(100), was observed. The critical thickness at which the spin reorientation transition from perpendicular to in-plane easy axis starts, is found to be 3.5 ML for RT-grown Fe/Cu 3 Au(100) as compared with 5.5 ML for the LT-grown films on both substrates.