Nanoscale diffusion at the interfaces in multilayers plays a vital role in controlling their physical properties for a variety of applications. In the present work depth-dependent interdiffusion in a Si/Fe/Si trilayer has been studied with sub-nanometer depth resolution, using x ray standing waves. High depth-selectivity of the present technique allows one to measure diffusion at the two interfaces of Fe namely, Fe-on-Si and Si-on-Fe, independently, yielding an intriguing result that Fe diffusivity at the two interfaces is not symmetric. It is faster at the Fe-on-Si interface. While the values of activation energy at the two interfaces are comparable, the main difference is found in the pre-exponent factor suggesting different mechanisms of diffusion at the two interfaces. This apparently counter-intuitive result has been understood in terms of an asymmetric structure of the interfaces as revealed by depth selective conversion electron Mössbauer spectroscopy. A difference in the surface free energies of Fe and Si can lead to such differences in the structure of the two interfaces.

The effect of interface roughness on exchange-bias (EB) properties of polycrystalline Co/CoO bilayer structure has been studied in-situ. Isothermal annealing of a 135 Å thick Co layer under the partial pressure of pure oxygen at 573 K results in the formation of a 35 Å thick CoO layer, the surface roughness of which increases with the increasing annealing time. Bilayers were characterized in-situ using magneto-optic Kerr effect, reflection high energy electron diffraction, and x-ray reflectivity for their magnetic and structural properties during each stage of bilayer growth. Combined analysis revealed that the increase in the roughness from 7 ±0.5 Å to 13 ±Å causes the exchange bias field (HEB) to decrease from 171 Oe to 81 Oe, whereas coercivity (HC) increases up to 616 Oe. In contrast to some earlier studies on polycrystalline films, where HEB increased with roughness due to the increase in the uncompensated spins at ferromagnetic-antiferromagnetic (AFM) layer interface, in the present case, dependence of HEB and HC on the roughness is attributed to the disorder at the interface of AFM layer, which leads to a decrease in HEB due to weakening of the effective spin coupling at the interface. Present in-situ experiments make it possible to study the variations in EB properties with the interface roughness in a single sample, and thus avoiding the possibility of the sample to sample variation in the morphological properties along with the change in the interface roughness.

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It is demonstrated that interface structure in thin film nanostructures can be studied with a depth resolution of a fraction of a nanometer by using x-ray standing waves generated by a multilayer mirror used as a substrate. Two interfaces of a few nm thick Fe layer in magnetic trilayer structures Tb/ Fe/ Tb and Cr/ Fe/ Cr could be clearly resolved using x-ray standing waves generated by an underlying W / Si multilayer mirror. It is found that in both the cases rms roughness of the two interfaces Fe-on-Tb͑Cr͒ and Tb͑Cr͒-on-Fe are not equal. For example, roughness of Fe-on-Tb interface is 1.2 nm, while that of Tb-on-Fe interface is 0.7 nm. The technique is particularly suitable in systems in which x-ray scattering contrast between adjacent layers is poor.

In-situ magneto-optical Kerr effect measurements have been done to study the evolution of the magnetic properties of ultrathin cobalt films on MgO(001)surface. A magnetic dead layer is found to exist at the MgO/Co interface, thickness of which is influenced by possible surface contamination of MgO substrate. X-ray photoelectron spectroscopy measurements show that etching the substrate with 500 eV Ar ions results in partial removal of carbon contamination. A lower carbon contamination results in reduction of the thickness of dead layer from 2.2 nm to 1.3 nm. At thicknesses below 3 nm, Co islands exhibit superparamagnetic relaxation. For higher film thickness, a well-defined uniaxial magnetic anisotropy develops along (100) direction.