A p-type Heusler compound: Growth, structure, and properties of epitaxial thin NiYBi films on MgO(100)

Epitaxial semiconducting NiYBi thin films were directly prepared on MgO(100) substrates by magnetron sputtering. The intensity ratio of the (200) and (400) diffraction peaks, I(200)/I(400) = 2.93, was close to the theoretical value (3.03). The electronic structure of NiYBi was calculated using WIEN2k and a narrow indirect band gap of width 210 meV was found. The valence band spectra of the films obtained by linear dichroism in hard X-ray photoelectron spectroscopy exhibit clear structures that are in good agreement with the calculated band structure of NiYBi

Improving thermoelectric performance of TiNiSn by mixing MnNiSb in the half-Heusler structure

The thermoelectric properties of n type semiconductor, TiNiSn is optimized by partial substitution with metallic, MnNiSb in the half Heusler structure. Herein, we study the transport properties and intrinsic phase separation in the system. The Ti1-xMnxNiSn1-xSbx alloys were prepared by arc-melting and were annealed at temperatures obtained from differential thermal analysis and differential scanning calorimetry results. The phases were characterized using powder X-ray diffraction patterns, energy dispersive X-ray spectroscopy, and differential scanning calorimetry. After annealing the majority phase was TiNiSn with some Ni rich sites and the minority phases was majorly Ti6Sn5, Sn, and MnSn2. Ni rich sites were caused by Frenkel defects, this led to a metal-like behavior of the semiconducting specimens at low temperature. For x up to 0.05 the samples showed an activated conduction, whereas for x>0.05 they showed metallic character. The figure of merit for x=0.05 was increased by 61% (ZT=0.45) in comparison to the pure TiNiSn.Comment: 7 pages and 5 figures. Submitted to Physical Chemistry Chemical Physics - RSC Publishing on 6th of October, 201

Highly selective recovery of Ni(II) in neutral and acidic media using a novel Ni(II)-ion imprinted polymer

In this work, an original ion-imprinted polymer (IIP) was synthetized for the highly selective removal of Ni(II) ions in neutral and acidic media. First a novel functional monomer (AMP-MMA) was synthetized through the amidation of 2-(aminomethyl)pyridine (AMP) with methacryloylchloride. Following Ni(II)/AMP-MMA complex formation study, the Ni(II)-IIP was produced via inverse suspension polymerization (DMSO in mineral oil) and characterized with solid state 13C CPMAS NMR, FT-IR, SEM and nitrogen adsorption/desorption experiments. The Ni(II)-IIP was then used in solid-phase extraction of Ni(II) exploring a wide range of pH (from neutral to strongly acidic solution), several initial concentrations of Ni(II) (from 0.02 to 1 g/L), and the presence of competitive ions (Co(II), Cu(II), Cd(II), Mn(II), and Mg(II)). The maximum Ni(II) adsorption capacity at pH 2 and pH 7 reached values of 138.9 mg/g and 169.5 mg/g, that are among the best reported in literature. The selectivity coefficients toward Cd(II), Mn(II), Co(II), Mg(II) and Cu(II) are also very high, with values up to 38.6, 32.9, 25.2, 23.1 and 15.0, respectively. The Ni(II)-IIP showed good reusability of up to 5 cycles both with acidic and basic Ni(II) eluents.Peer reviewe

Investigation on Mn3−δ_{3-\delta}Ga/MgO interface for magnetic tunneling junctions

The Mn$_3$Ga Heusler compound and related alloys are the most promising materials for the realization of spin-transfer-torque switching in magneto tunneling junctions. Improved performance can be achieved by high quality interfaces in these multilayered structured devices. In this context, the interface between Mn$_{1.63}$Ga and MgO is of particular interest because of its spin polarization properties in tunneling junctions. We performed a chemical characterization of the MgO/Mn$_{1.63}$Ga junction by hard x-ray photoelectron spectroscopy (HAXPES). The experiment indicated the formation of Ga-O bonds at the interface and evidenced changes in the local environment of Mn atoms in the proximity of the MgO film. In addition, we show that the insertion of a metallic Mg-layer interfacing the MgO and Mn--Ga film strongly suppresses the oxidation of gallium

High energy, high resolution photoelectron spectroscopy of Co2Mn(1-x)Fe(x)Si

This work reports on high resolution photoelectron spectroscopy for the valence band of Co2Mn(1-x)Fe(x)Si (x=0,0.5,1) excited by photons of about 8 keV energy. The measurements show a good agreement to calculations of the electronic structure using the LDA+U scheme. It is shown that the high energy spectra reveal the bulk electronic structure better compared to low energy XPS spectra. The high resolution measurements of the valence band close to the Fermi energy indicate the existence of the gap in the minority states for all three alloys.Comment: 14 pages, 5 figures, submitted to J. Phys. D: Appl. Phy

Evidence for Localized Moment Picture in Mn-based Heusler Compounds

X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) were used to probe the oxidation state and element specific magnetic moments of Mn in Heusler compounds with different crystallographic structure. The results were compared with theoretical calculations, and it was found that in full Heusler alloys, Mn is metallic (oxidation state near 0) on both sublattices. The magnetic moment is large and localized when octahedrally coordinated by the main group element, consistent with previous theoretical work, and reduced when the main group coordination is tetrahedral. By contrast, in the half Heusler compounds the magnetic moment of the Mn atoms is large and the oxidation state is +1 or +2. The magnetic and electronic properties of Mn in full and half Heusler compounds are strongly dependent on the structure and sublattice, a fact that can be exploited to design new materials.Comment: 15 pages, 4 figure

Primary vs. secondary curved fold axes: Deciphering the origin of the Aït Attab syncline (Moroccan High Atlas) using paleomagnetic data

The Aït Attab syncline, located in the Central High Atlas, displays a curved geometry in plan view, and is considered as one of the most spectacular fold shapes in the Central High Atlasic belt. We conducted a paleomagnetic study in Jurassic-Cretaceous red beds to investigate the origin of this geometry. The Natural Remanent Magnetization (NRM) is dominated by a secondary magnetization carried by haematite with unvarying normal polarity that has been dated at about 100 Ma. The regional fold test performed in both limbs of the syncline is positive and the paleomagnetic vectors (after tectonic correction) are parallel throughout the curvature, indicating a negative oroclinal bending test. These results are inconsistent with previous works that consider the bent geometry of this syncline to result from subsequent distortion of originally NE–SW trending structures by rotation about a vertical axis. We interpret the NRM data to demonstrate that the changing trend of the Aït Attab syncline is a primary feature, resulting from the influence of pre-existing, NE–SW and E-W-striking extensional faults that developed during a strike-slip regime. Paleomagnetic results also reveal that the tilting observed in the sampled red beds is post Albian, probably linked to the Cenozoic inversion of the High Atlasic belt