Search results for "Surfaces"

Terahertz spectroscopy for all-optical spintronic characterization of the spin-Hall-effect metals Pt, W and Cu80Ir20

2018

Identifying materials with an efficient spin-to-charge conversion is crucial for future spintronic applications. In this respect, the spin Hall effect is a central mechanism as it allows for the interconversion of spin and charge currents. Spintronic material research aims at maximizing its efficiency, quantified by the spin Hall angle and the spin-current relaxation length . We develop an all-optical contact-free method with large sample throughput that allows us to extract and . Employing terahertz spectroscopy and an analytical model, magnetic metallic heterostructures involving Pt, W and Cu80Ir20 are characterized in terms of their optical and spintronic properties. The validity of our …

Correlation of local disorder and electronic properties in the Heusler alloy Co2Cr0.6Fe0.4Al

2007

For the fully ordered Heusler alloy Co2Cr0.6Fe0.4Al half-metallic ferromagnetism has been predicted. Local disorder other than the Al–Cr/Fe (B2)-type disorder is known to destroy the half-metallic bandgap. The usage of appropriate buffer layers improves the structural quality of thin films. We correlate the structural properties of thin magnetron sputtered films determined by x-ray diffraction with details of the x-ray magnetic circular dichroism spectra. From the value of the magnetic moment located at the Cr atom and features of the Co absorption spectra we conclude that the buffer layers lead also to an improvement in the local atomic order. The atomic ordering gradually approaches the l…

Influence of laser–target interaction regime on composition and properties of surface layers grown by laser treatment of Ti plates

2009

Surface laser treatment of commercially pure titanium plates was performed in air using two different Nd : YAG sources delivering pulses of 5 and 35 ns. The laser fluence conditions were set to obtain with each source either yellow or blue surface layers. Nuclear reaction analysis (NRA) was used to quantify the amount of light elements in the formed layers. Titanium oxinitrides, containing different amounts of oxygen and nitrogen, were mainly found, except in the case of long pulses and high laser fluence, which led to the growth of titanium dioxide. The structure of the layers was studied by x-ray diffraction and Raman spectroscopy. In addition, reflectance spectra showed the transition fr…

Covalent bonding and the nature of band gaps in some half-Heusler compounds

2005

Half-Heusler compounds \textit{XYZ}, also called semi-Heusler compounds, crystallize in the MgAgAs structure, in the space group $F\bar43m$. We report a systematic examination of band gaps and the nature (covalent or ionic) of bonding in semiconducting 8- and 18- electron half-Heusler compounds through first-principles density functional calculations. We find the most appropriate description of these compounds from the viewpoint of electronic structures is one of a \textit{YZ} zinc blende lattice stuffed by the \textit{X} ion. Simple valence rules are obeyed for bonding in the 8-electron compound. For example, LiMgN can be written Li$^+$ + (MgN)$^-$, and (MgN)$^-$, which is isoelectronic wi…

Cluster issue on Heusler compounds and devices

2009

Swift-ion-induced hardening and reduction of dislocation mobility in LiF crystals

2008

Ion-induced change in Vickers hardness and arm length of dislocation rosettes created by indentation on the (1 0 0) face of LiF crystals was studied. The irradiations were performed using swift U, Bi and Ni ions with a specific energy of 11 MeV per nucleon at fluences between 106 and 1013 ions cm−2. Remarkable effects of the ion-induced hardening and reduction of dislocation arm length were observed above the threshold fluences of about 109–1010 ions cm−2 and 106–107 ions cm−2, respectively. The products of track core damage and aggregates of single defects in the halo of overlapping tracks are responsible for the effects. The results are analysed using the Orowan's model of dislocation imp…

Exchange bias in epitaxial Mn2Au (0 0 1)/Fe (0 0 1) bilayers

2019

Grain size effect and local disorder in polycrystalline relaxors via scanning probe microscopy

2007

Local piezoresponse of individual grains in polycrystalline Pb0.9125La0.0975(Zr0.65Ti0.35)0.976O3 (PLZT 9.75/65/35) relaxor ceramics is studied using the scanning probe microscopy (SPM) technique. The observed piezoelectric contrast consisting of irregular (labyrinth-type) polarization patterns is attributed to the compositional disorder and consequent charge imbalance caused by high La concentration. A measure of this disorder, the polarization correlation length ξ, is directly determined using an autocorrelation analysis function implemented in the SPM software. The analysis of the obtained images shows that ξ taken at the scale ~200 nm varies as a function of the position inside the grai…

Epitaxial Mn2Au thin films for antiferromagnetic spintronics

2015

Mn2Au is one of the few candidate materials for antiferromagnetic spintronics requiring ordered metals with a high Neel-temperature and strong spin–orbit coupling. We report the preparation of epitaxial Mn2Au thin films by rf-sputtering. Structural characterization by x-ray and electron diffraction demonstrates a high degree of atomic order and the temperature dependence of the resistivity is typical for a good metal. The magnetic properties of the samples are studied by the investigation of Mn2Au/Fe bilayers. Exchange bias effects are observed, which present strong evidence for antiferromagnetic order in the Mn2Au thin films. Small domains of 500 nm are visualized in the exchange coupled F…

Influence of plasma chemistry on impurity incorporation in AlN prepared by plasma enhanced atomic layer deposition

2013

Impurities in aluminum nitride films prepared by plasma enhanced atomic layer deposition using NH3-, N2/H2- and N2-based plasmas are investigated by combining time-of-flight elastic recoil detection analysis (ERDA) and Fourier transform infrared spectroscopy. Different atomistic growth mechanisms are found to exist between the plasma chemistries. N2-plasma is shown as not suitable for the low-temperature deposition of AlN. Films deposited by NH3- and N2/H2-based processes are nitrogen rich and heavily hydrogenated. Carbon impurities exist at higher concentrations for the N2/H2-processes. The discovery of nitrile groups in the films indicates that carbon impurities can be partially attribute…