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The tunnel magnetoresistance ratio (TMR) of fully epitaxial magnetic tunnel junctions with an off- stoichiometric Co2MnSi Heusler alloy has been shown to exhibit a systematic dependence on Mn content, reaching 1135% at 4.2 K for Co2Mn1.29Si. In this paper, we explain the behaviorof the observed TMR ratio using ab initio calculations and hard x-ray photoelectron spectroscopy (HAXPES). For the Mn-deficient samples, we show that the the drop of the TMR is caused by Co antisite atoms, which impose extra states into the minority-spin band gap. On the other hand, Mn-excess composition shows nearly half-metallic behavior. This result can be intuitively understood since both Co2MnSi and Mn2CoSi are theoretically predicted to be half-metallic ferromagnets. [ABSTRACT FROM AUTHOR]

This work reports the measurement of magnetic dichroism in angular-resolved photoemission from in-plane magnetized buried thin films. The high bulk sensitivity of hard x-ray photoelectron spectroscopy (HAXPES) in combination with circularly polarized radiation enables the investigation of the magnetic properties of buried layers. HAXPES experiments with an excitation energy of 8 keV were performed on exchange-biased magnetic layers covered by thin oxide films. Two types of structures were investigated with the IrMn exchange-biasing layer either above or below the ferromagnetic layer: one with a CoFe layer on top and another with a Co2FeAl layer buried beneath the IrMn layer. A pronounced magnetic dichroism is found in the Co and Fe 2p states of both materials. The localization of the magnetic moments at the Fe site conditioning the peculiar characteristics of the Co2FeAl Heusler compound, predicted to be a half-metallic ferromagnet, is revealed from the magnetic dichroism detected in the Fe 2p states. [ABSTRACT FROM AUTHOR]

The electronic band structure of thin films and superlattices made of Heusler compounds with NiTiSn and NiZr0.5Hf0.5Sn composition was studied by means of polarization dependent hard x-ray photoelectron spectroscopy. The linear dichroism allowed to distinguish the symmetry of the valence states of the different types of layered structures. The films exhibit a larger amount of "in-gap" states compared to bulk samples. It is shown that the films and superlattices grown with NiTiSn as starting layer exhibit an electronic structure close to bulk materials. [ABSTRACT FROM AUTHOR]

Mn2NiGa is reported to be a shape memory material with a martensite-austenite phase transition. Temperature dependent measurements of the transport and magnetic properties reveal the martensitic transition close to room temperature with a thermal hysteresis of about 27 K. The electronic structure of the valence band in both phases was studied by hard x-ray photoelectron spectroscopy. The results clearly indicate that strong changes in the electronic structure appear at the phase transition. [ABSTRACT FROM AUTHOR]

Besides of their well-known wide range of properties it was recently shown that many of the heavy Heusler semiconductors with 1:1:1 composition and C1b structure exhibit a zero band gap behavior and are topological insulators induced by their inverted band structure. In the present study, the electronic structure of the Heusler compounds PtYSb and PtLaBi was investigated by bulk sensitive hard x-ray photoelectron spectroscopy. The measured valence band spectra are clearly resolved and in well agreement to the first-principles calculations of the electronic structure of the compounds. The experimental results give clear evidence for the zero band gap state. [ABSTRACT FROM AUTHOR]

The effect of Ti substitution by Sc on the thermoelectric properties of the Heusler compounds NiTi0.3-xScxZr0.35Hf0.35Sn (where 00.3Zr0.35Hf0.35Sn showed n-type conductivity with a Seebeck coefficient of -288 μV/K at 350 K, while under Sc substitution the system switched to p-type behavior. A maximum Seebeck coefficient of +230 μV/K (350 K) was obtained by 4% Sc substitution, which is the highest value for p-type thermoelectric compounds based on Heusler alloys. The electronic structure was studied by photoelectron spectroscopy excited by hard x-ray synchrotron radiation. Massive in gap states are observed for the parent compound. This proves that the electronic states close to the Fermi energy play a key role on the behavior of the transport properties. Especially, they are responsible for the high, negative Seebeck coefficient of the parent compound. [ABSTRACT FROM AUTHOR]

This work reports on hard x-ray photoelectron spectroscopy (HAXPES) of CoFeB based tunnel junctions. Aim is to explain the role of the boron diffusion for the observed improvement of the tunneling magnetoresistance ratio with increasing annealing temperature. The high bulk sensitivity of HAXPES was used as a nondestructive technique to analyze CoFeB–MgO–CoFeB magnetic tunnel junctions. The investigated samples were processed at different annealing temperatures from 523 to 923 K. Hard x-ray core level spectroscopy reveals an enforced diffusion of boron from the CoFeB into the adjacent Ta layer with increasing annealing temperature. The dependence of the tunneling magnetoresistance on the annealing temperature is explained by the combined effects of an improved crystalline structure together with a change in the spin polarization at the Fermi energy caused by the removal of boron from the CoFeB layer and Ta diffusion at high annealing temperature. [ABSTRACT FROM AUTHOR]

The spin-resolved electronic structure of buried magnetic layers is studied by hard X-ray photoelectron spectroscopy (HAXPES) using a spin polarimeter in combination with a high-energy hemispherical electron analyzer at the high-brilliance BL47XU beamline (SPring-8, Japan). Spin-resolved photoelectron spectra are analyzed in comparison with the results of magnetic linear and circular dichroism in photoelectron emission in the case of buried Co2FeAl0.5Si0.5 layers. The relatively large inelastic mean free path (up to 20 nm) of fast photoelectrons enables us to extend the HAXPES technique with electron-spin polarimetry and to develop spin analysis techniques for buried magnetic multilayers and interfaces. [ABSTRACT FROM AUTHOR]

The quaternary intermetallic Heusler compounds CoFeMnZ (Z = Al, Ga, Si, or Ge) with 1 : 1 : 1 : 1 stoichiometry were predicted to exhibit half-metallic ferromagnetism by ab initio electronic structure calculations. The compounds were synthesized using an arc-melting technique and the crystal structures were analyzed using x-ray powder diffraction. The electronic properties were investigated using hard x-ray photoelectron spectroscopy. The low-temperature magnetic moments, as determined from magnetization measurements, follow the Slater-Pauling rule, confirming the proposed high spin polarizations. All compounds have high Curie temperatures, allowing for applications at room temperature and above. [ABSTRACT FROM AUTHOR]

Abstract: Due to their exceptional thermoelectric properties Half-Heusler alloys like MNiSn (M=Ti,Zr,Hf) have moved into focus. The growth of single crystalline thin film TiNiSn and Zr0.5Hf0.5NiSn by dc magnetron sputtering is reported. Seebeck and resistivity measurements were performed and their dependence on epitaxial quality is shown. Seebeck coefficient, specific resistivity and power factor for Zr0.5Hf0.5NiSn at room temperature were measured to be 63μVK−1, 14.1μΩm and 0.28mWK−2 m−1, respectively. Multilayers of TiNiSn and Zr0.5Hf0.5NiSn are promising candidates to increase the thermoelectric figure-of-merit by decreasing thermal conductivity perpendicular to the interfaces. The epitaxial growth of multilayers containing TiNiSn and Zr0.5Hf0.5NiSn is demonstrated by measuring satellite peaks in the X-ray diffraction pattern originating from the additional symmetry perpendicular to the film surface. [Copyright &y& Elsevier]

This work reports on the electronic and crystalline structure and the mechanical, magnetic, and transport properties of the polycrystalline Heusler compound Co2MnGe. The crystalline structure was examined in detail by extended x-ray absorption fine-structure spectroscopy and anomalous x-ray diffraction. The compound exhibits a well-ordered L21 structure as is typical for Heusler compounds with 2:1:1 stoichiometry. The low-temperature magnetic moment agrees well with the Slater-Pauling rule and indicates a half-metallic ferromagnetic state of the compound, as is predicted by ab initio calculations. Transport measurements and hard x-ray photoelectron spectroscopy were performed to explain the electronic structure of the compound. The obtained valence band spectra exhibit small energy shifts that are the result of the photoexcitation process, whereas electron-electron correlation in the ground state is negligible. The vibration and mechanical properties of the compound were calculated. The observed hardness values are consistent to a covalent-like bonding of Co2MnGe. [ABSTRACT FROM AUTHOR]