We report on the magnetic reversal characteristics of exchange coupled ferrimagnetic (FI) Tb 19 Fe 81 /Tb 36 Fe 64 heterostructures. Both layers are amorphous and exhibit strong perpendicular magnetic anisotropy. The investigated heterostructures consist of a Tb-dominated and a Fe-dominated FI layer. Thus, in the magnetic ground state the net moments of the individual layers are oppositely aligned due to antiferromagnetic coupling of Fe and Tb moments. By cooling the system below 160 K, a large positive and negative exchange bias (EB) effect appears for the Tb-and Fe-dominated layers, respectively. The biasing depends only on the initial magnetization state and is neither affected by a cooling field nor by loop cycling. The phenomenon can be explained by the presence of a hard magnetic Fe-dominated interfacial layer, which forms during the sputter deposition process due to interface mixing and resputtering effects. This interfacial layer acts as a pinning layer below a certain temperature, where its coercivity increases to values larger than the accessible magnetic field range. This assumption is further supported by introducing a 0.9-nm-thick Ru spacer layer, which causes the EB effect to vanish. The EB effect was further investigated for a sample series, where the thickness ratio of the two Tb-Fe layers was varied, while keeping the total thickness of the bilayers constant. Only samples where the individual layers are sufficiently thick reveal double shifted loops, indicating the high sensitivity of the observed bias effect with respect to the magnetic properties of the individual layers and their interfacial area.

We report experimental evidence for the violation of the "diffusional parabolic law" ͑x ϰ t 0.5 , where x is the interface shift and t is time͒ as predicted recently by computer simulation ͓Z. Erdélyi et al., Phys. Rev. B 69, 113407 ͑2004͔͒ for a binary system with restricted mutual solubility. Using x-ray photoelectron spectroscopy we investigated the shift of the interface between a thin Ni layer ͑3 nm͒ deposited under UHV conditions on top of a Au͑111͒ single crystal during its thermally driven dissolution into the Au substrate. From the temporal evolution of the Ni-2p and Au-4f core level intensities at various fixed temperatures, a power law could be extracted for the time dependence of the interface shift ͑ϰt k c ͒ with exponents in the range of 0.6-0.7. Thus, clear experimental evidence is provided that the kinetics of such a shift might differ from the well known parabolic law if restricted to the nanometer scale.

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Kinetic pathways of diffusion and solid state reactions in nanostructured thin film systemsMass transport and solid state reactions in nanocrystalline thin films is reviewed.It is illustrated that diffusion along different grain boundaries, GB, can have important effects on the overall intermixing process between two pure films.These processes can be well characterized by a bimodal GB network, with different (fast and slow) diffusivities. First the atoms migrate along fast GBs (triple junctions) and accumulate at the film surface. These accumulated atoms form a secondary diffusion source for back diffusion along slow boundaries.Thus the GBs of the thin films can be gradually filled up with the diffusing atoms and composition depth profiles reflect the result of these processes. Similar process can be observed in binary systems with intermetallic layers: instead of nucleation and growth of the reaction layer at the initial interface, the reaction takes place in the GBs and the amount of the product phase growths by the motion of its interfaces perpendicular to the GBs. Thus, the entire layer of the pure parent films can be consumed by this GB diffusion induced solid state reaction (GBDIREAC), and a fully homogeneous product layer can be obtained.

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The solid-state reaction in Pt(15 nm)/Fe(15 nm) and Pt(15 nm)/Ag(10 nm)/Fe(15 nm) thin films after postannealing at 593 K and 613 K for different annealing times has been studied. The structural properties of these samples were investigated by various methods including depth profiling with secondary neutral mass spectrometry, transmission electron microscopy, and X-ray diffraction. It is shown that after annealing at the above temperatures where the bulk diffusion processes are still frozen, homogeneous reaction layers of FePt and FePt with about 10 at.% Ag, respectively, have been formed. Corresponding depth profiles of the element concentrations revealed strong evidence that the formation mechanism is based on a grain boundary diffusion induced solid-state reaction in which the reaction interfaces sweep perpendicularly to the original grain boundary. Interestingly, X-ray diffraction indicated that in both thin-film systems after the solid-state reaction the ordered L1 0 FePt

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