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We present experimental evidence for a controlled movement of single atoms of Co incorporated in a Cu(0 0 1) surface under the influence of a scanning tunnelling microscope (STM) tip. The Co atoms move preferentially along such [1 1 0] nearest neighbour directions in the Cu surface which lie in an acute angle to the vertical sweep direction of the STM tip. The induced motion of the Co atoms is controllable by the tip bias voltage. We propose that a tip mediated surface vacancy exchange process is responsible for the observed motion of the impurity atoms. [Copyright &y& Elsevier]

A comprehensive analysis of the giant in-plane uniaxial magnetic anisotropy of exchange biased molecular beam epitaxy grown Cu(1 1 0)/Ni80Fe20/Fe50Mn50 bilayers, discovered by Jungblut et al. (J. Appl. Phys. 75 (1994) 6659) is presented. Cu(1 1 0)/Ni80Fe20 samples have a uniaxial in-plane volume anisotropy with a [0 0 1] easy axis direction. Covering such ferromagnetic (F) layers with an antiferromagnetic (AF) Fe50Mn50 layer introduces an interface contribution to the uniaxial anisotropy that leads to an [1 1¯ 0] easy axis direction for F layer thicknesses below a critical value of 4 nm, and to an enhancement of the [0 0 1] anisotropy for larger thicknesses. The effect occurs only for Fe50Mn50 layers that are thicker than the minimum thickness that is required to obtain the exchange bias effect. From in situ low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) the Ni80Fe20 surface is shown to be corrugated, viz. in the form of elongated 2–4 monolayer high mesas at a distance of typically 4–8 nm in the [0 0 1] direction and a length along the [1 1¯ 0] direction of 25–60 nm. We show that this novel mesoscopic magnetic effect can be explained from the magnetically uncompensated nature of the AF (1 1 0) surface in combination with the corrugation of the F/AF interface. The spatially varying sign of the F–AF exchange coupling then leads to a preferred F layer magnetization direction that is perpendicular to the staggered AF magnetization. The remarkable change of sign of the interface anisotropy indicates that in the thin and thick F layer regimes the staggered AF magnetizations that are frozen in during the growth are different by a 90° rotation. We tentatively explain this from the kinetics of magnetic structure transformations in the bilayer during the growth process. The local exchange bias interaction parameter obtained from a quantitative analysis is Jeb,loc≈2.5–10 mJ/m2, which is close to the theoretical upper limit and is two orders of magnitude larger than the sample averaged interaction parameter, Jeb, obtained from the exchange bias field. This provides the first direct experimental proof that the observed value of Jeb of an AF/F bilayer can be the result of much larger but almost completely averaged out opposing local AF–F exchange interactions. The paper contains a brief overview of the recent developments in the field of mesoscopic magnetism. [Copyright &y& Elsevier]

The ordering of an organic molecular layer on a ferromagnetic substrate is studied using scanning tunnelling microscopy. Highly ordered layers of perylene-tetracarboxylic-dianhydride (PTCDA) were prepared by vacuum sublimation on an oxygen precovered Ni(1 1 1) surface. The structure of thin layers of PTCDA deposited at room temperature was investigated as a function of growth rates and thickness. It is demonstrated that oxygen passivation reduces the reactivity sufficiently to lead to well-ordered overlayers of PTCDA. For thin films grown at low deposition rates, a herringbone-like structure has been observed. This structure is consistently observed in the islands with typically 100 nm in diameter and 1–2 ML thickness. Depositing thicker films at higher deposition rates results in polycrystalline islands. Within the polycrystalline islands two distinct stripe-like phases are observed in domains with a lateral size of typically 10 nm. The potential impact of these results for organo-metallic spintronic devices is addressed. [Copyright &y& Elsevier]