We study the effect of bilayer thickness at fixed volume fraction on the structural quality of Fe/V (001)superlattices. We find that such artificial metallic superlattices can be manufactured with excellent crystalquality and layering up to at least 50 Å in repeat distance (K = LFe +LV). For an intended fixed ratio of theconstituents: LFe/LV= 1/7, out-of-plane coherence lengths comparable to the thicknesses of the sampleswere obtained. We evaluate the strain in- and out-of-plane of both layers as a function of the bilayer thicknessand comment on the growth using the framework of linear elasticity theory. We interpret the stabilityof the superlattice against crystal degradation due to the alternating compressive and tensile strain, yieldingclose to ideal lattice matching to the substrate.

We investigate the hysteresis obtained in the hydrogen absorption and desorption cycle for a single crystal Pd/V-28 [Fe-4/V-28](11) superlattice. Below the critical temperature, a small but clear hysteresis is observed in the pressure-composition isotherms, while it is absent above. The experimental results thereby prove the relevance of macroscopic energy barriers for obtaining hysteresis in coherent structural transformations. The textured Pd layer exhibits substantially larger hysteresis effects, which can be related to an irreversible energy loss caused by defect generation in Pd.

We investigate the effect of finite size on the chemical diffusion of deuterium in extremely thin V(001) layers. A five fold increase in the diffusion coefficient is observed at concentrations around 0.2 [D/V], when the thickness of the V is decreased from 28 to 14 atomic layers (approximate to 2.1-4.2 nm). The size dependent deuterium-deuterium interaction energy is argued to be the root of the observed changes as the diffusion rates are similar at low concentrations. The results demonstrate the feasibility of using finite-size effects to enhance the chemical diffusion of light interstitials in solids. We discuss the general applicability of these effects to other systems.

We investigate the effect of site occupancy on the chemical diffusion of hydrogen in strained vanadium. The diffusion rate is found to decrease substantially, when hydrogen is occupying octahedral sites as compared to tetrahedral sites. Profound isotope effects are observed when comparing the diffusion rate of H and D. The changes in the diffusion rate are found to be strongly influenced by the changes in the potential energy landscape, as deduced from first-principles molecular dynamics calculations.

While the performance of magnetic tunnel junctions based on metal/oxide interfaces is determined by hybridization, charge transfer, and magnetic properties at the interface, there are currently only limited experimental techniques with sufficient spatial resolution to directly observe these effects simultaneously in real-space. In this letter, we demonstrate an experimental method based on Electron Magnetic Circular Dichroism (EMCD) that will allow researchers to simultaneously map magnetic transitions and valency in real-space over interfacial cross-sections with sub-nanometer spatial resolution. We apply this method to an Fe/MgO bilayer system, observing a significant enhancement in the orbital to spin moment ratio that is strongly localized to the interfacial region. Through the use of first-principles calculations, multivariate statistical analysis, and Electron Energy-Loss Spectroscopy (EELS), we explore the extent to which this enhancement can be attributed to emergent magnetism due to structural confinement at the interface. We conclude that this method has the potential to directly visualize spin and orbital moments at buried interfaces in magnetic systems with unprecedented spatial resolution.

We present a direct experimental investigation of the thermal ordering in an artificial analogue of an asymmetric two-dimensional Ising system composed of a rectangular array of nano-fabricated magnetostatically interacting islands. During fabrication and below a critical thickness of the magnetic material the islands are thermally fluctuating and thus the system is able to explore its phase space. Above the critical thickness the islands freeze-in resulting in an arrested thermalized state for the array. Determining the magnetic state we demonstrate a genuine artificial two-dimensional Ising system which can be analyzed in the context of nearest neighbor interactions.

The research on complex hydrides for hydrogen storage was initiated by the discovery of Ti as a hydrogen sorption catalyst in NaAlH4 by Boris Bogdanovic in 1996. A large number of new complex hydride materials in various forms and combinations have been synthesized and characterized, and the knowledge regarding the properties of complex hydrides and the synthesis methods has grown enormously since then. A significant portion of the research groups active in the field of complex hydrides is collaborators in the International Energy Agreement Task 32. This paper reports about the important issues in the field of complex hydride research, i.e. the synthesis of borohydrides, the thermodynamics of complex hydrides, the effects of size and confinement, the hydrogen sorption mechanism and the complex hydride composites as well as the properties of liquid complex hydrides. This paper is the result of the collaboration of several groups and is an excellent summary of the recent achievements.

The electron energy-loss spectroscopy technique known as electron magnetic circular dichroism (EMCD) has enormous potential for quantitatively probing the magnetic behavior of materials on the nanoscale. However, the requirement for mostly parallel illumination conditions greatly complicates the extraction of EMCD signals from surface areas under a few square nanometers, because scanning probe methods are limited to around this spatial resolution by the need for higher convergence angles. Here we propose theoretically and demonstrate experimentally that EMCD detection is feasible with convergence angles that are sufficiently large even for atomic resolution spectroscopy. Utilizing scanning transmission electron microscopy we experimentally detect a clear EMCD signal from a 50-nm-thick sample of bcc iron using a convergence semiangle of 8 mrad at 300 keV acceleration voltage, resulting in a probe size of approximately 2 angstrom. We subsequently estimate the number of chirally scattered electrons needed for an unambiguous detection of the EMCD signal and present a method to quantify confidence in signal detection.

We report on a discrete layer-by-layer magnetic switching in Fe/MgO superlattices driven by an antiferromagnetic interlayer exchange coupling. The strong interlayer coupling is mediated by tunneling through MgO layers with thicknesses up to at least 1.8 nm, and the coupling strength varies with MgO thickness. Furthermore, the competition between the interlayer coupling and magnetocrystalline anisotropy stabilizes both 90 degrees and 180 degrees periodic alignment of adjacent layers throughout the entire superlattice. The tunable layer-by-layer switching, coupled with the giant tunneling magnetoresistance of Fe/MgO/Fe junctions, is an appealing combination for three-dimensional spintronic memories and logic devices.

For a high magnetic refrigeration efficiency, a large change of magnetic entropy (-Delta S-M) associated with a high relative cooling power (RCP) are highly desirable. Here, the ion implantation is used to enhance both parameters in FeZr amorphous films. A considerable enhancement of both (-Delta S-M) and RCP, from 0.66 to 1.01 J/kg K and 84.5 to 155.5 J/kg respectively, for the as-grown sample compared to the C -implanted sample is obtained for a magnetic field change of mu(0)Delta H = 1.5 T. The increase of (-Delta S-M) and RCP values, are attributed to the increase of the magnetization and the chemical inhomogeneity, respectively upon C implantation.