Effect of uniaxial strain on the site occupancy of hydrogen in vanadium from density-functional calculations

We investigate the influence of uniaxial strain on site occupancy of hydrogen vanadium, using density functional theory. The site occupancy is found to be strongly influenced by the strain state of the lattice. The results provide the conceptual framework of the atomistic description of the observed hysteresis in the alpha to beta phase transition in bulk, as well as the preferred octahedral occupancy of hydrogen in strained V layers

Double magnetic proximity in Fe/Fe0.32V0.68 superlattices

Publisher's version (útgefin grein)The conventional magnetic proximity effect and double-proximity effects were studied in a set of fully coherent high-quality Fe/Fe0.32V0.68 superlattices. Applying a simple model to the saturation magnetization, it is seen that the magnetic proximity effect is gigantic in magnitude in the alloy—the magnetization is enhanced by 20–450 % and the ordering temperature is enhanced by a factor of 2. The magnitude of the effect can be explained by the large susceptibility of the alloy above its intrinsic ordering temperature. Additionally, a strong dependence of the ordering temperature of single monolayers of Fe on the interlayer distance is observed. The results give insight into new ways of using alloying and large magnetic susceptibility combined with magnetic proximity effects to enhance the functionality of materials that are of interest for spintronic devices.F.M. acknowledges funding from the Icelandic Centrefor Research (Grant No. 174271-051). H.P. wishes to thankGiuseppe Muscas for fruitful discussions.Peer reviewe

The impact of nanoscale compositional variation on the properties of amorphous alloys

The atomic distribution in amorphous FeZr alloys is found to be close to random, nevertheless, the composition can not be viewed as being homogenous at the nm-scale. The spatial variation of the local composition is identified as the root of the unusual magnetic properties in amorphous Fe$_{Zahl}$1-xZr$_{x}$ alloys. The findings are discussed and generalised with respect to the physical properties of amorphous and crystalline materials

Emergent tri-criticality in magnetic metamaterials

Metallic discs engineered on the 100 nm scale have an internal magnetic texture which varies from a fully magnetized state to a vortex state with zero moment. The interplay between this internal structure and the inter-disc interactions is studied in magnetic metamaterials made of square arrays of the magnetic discs. The texture is modeled by a mesospin of varying length with O(2) symmetry and the inter-disc interaction by a nearest neighbour coupling between mesospins. The thermodynamic properties of the model are studied numerically and an ordering transition is found which varies from Kosterlitz-Thouless to first order via an apparent tri-critical point. The effective critical exponent characterising the finite size magnetization evolves from the value for the 2D-XY model to less than half this value at the tri-critical point. The consequences for future experiments both in and out of equilibrium are discussed.Comment: 10 pages, 9 figure

Influence of misfit strain on the physical properties of Fe thin films

We investigate the growth of thin Fe layers on MgAl$_2$O$_4$ (001) and MgO (001) substrates using dc magnetron sputtering. The crystal quality of Fe layers deposited on MgAl$_2$O$_4$ is found to be substantially higher as compared to Fe grown on MgO substrates. The effects of the crystal quality on the magnetic and electric transport properties are discussed.Comment: 8 pages, 6 figure

Hydrogen site occupancy and strength of forces in nano-sized metal hydrides

The dipole force components in nano-sized metal hydrides are quantitatively determined with curvature and x-ray diffraction measurements. Ab-initio density functional theory is used to calculate the dipole components and the symmetry of the strain field. The hydrogen occupancy in a 100 nm thick V film is shown to be tetrahedral with a slight asymmetry at low concentration and a transition to octahedral occupancy is shown to take place at around 0.07 [H/V] at 360 K. When the thickness of the V layer is reduced to 3 nm and biaxially strained, in a Fe_0.5V_0.5/V superlattice, the hydrogen unequivocally occupies octahedral z-like sites, even at and below concentrations of 0.02 [H/V]

Magnon softening in a ferromagnetic monolayer: a first-principles spin dynamics study

We study the Fe/W(110) monolayer system through a combination of first principles calculations and atomistic spin dynamics simulations. We focus on the dispersion of the spin waves parallel to the [001] direction. Our results compare favorably with the experimental data of Prokop et al. [Phys. Rev. Lett. 102, 177206], and correctly capture a drastic softening of the magnon spectrum, with respect to bulk bcc Fe. The suggested shortcoming of the itinerant electron model, in particular that given by density functional theory, is refuted. We also demonstrate that finite temperature effects are significant, and that atomistic spin dynamics simulations represent a powerful tool with which to include these.Comment: v1: 11 pages, 3 figures. v2: double column, 5 pages, 3 figures, typos corrected, references adde

Magnetic order and energy-scale hierarchy in artificial spin ice

In order to explain and predict the properties of many physical systems, it is essential to understand the interplay of different energy-scales. Here we present investigations of the magnetic order in thermalised artificial spin ice structures, with different activation energies of the interacting Ising-like elements. We image the thermally equilibrated magnetic states of the nano-structures using synchrotron-based magnetic microscopy. By comparing results obtained from structures with one or two different activation energies, we demonstrate a clear impact on the resulting magnetic order. The differences are obtained by the analysis of the magnetic spin structure factors, in which the role of the activation energies is manifested by distinct short-range order. This demonstrates that artificial spin systems can serve as model systems, allowing the definition of energy-scales by geometrical design and providing the backdrop for understanding their interplay.Comment: 8 pages, 5 figures (+ supplementary 6 pages, 4 figures

Giant magnetic proximity effect in amorphous layered magnets

Publisher's version (útgefin grein)Here we study the magnetic proximity effect in amorphous layered magnets of alternating high- and low-Tc materials using magnetometry and polarized neutron reflectivity. By altering the thickness of either the high- or low-Tc layer we are able to extract the induced magnetic moment in the low-Tc layer directly and study how it scales with thickness. We observe that the ordering temperature of the low-Tc layer is enhanced and above which a second magnetically ordered state with a very large extension is observed. This induced magnetic state survives to a temperature at least three times that of the ordering temperature of the low-Tc layer and the induced magnetization is approximately constant throughout at least a 10-nm-thick layer. The induced magnetic region within the low-Tc layer does not depend on the thickness of the adjacent high-Tc layer.This work was supported by the Icelandic Centre forResearch, Grant No. 174271-051, the University of IcelandResearch Fund, and the Swedish Research Council (VR).Peer reviewe