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Using momentum microscopy with sub

Using momentum microscopy with sub-µm spatial resolution, allowing momentum resolved photoemission on individual antiferromagnetic domains, we observe an asymmetry in the electronic band structure, E ( k ) ≠ E ( − k ) , in Mn2Au. This broken band structure parity originates from the combined time and parity symmetry, P T , of the antiferromagnetic order of the Mn moments, in connection with spin–orbit coupling. The spin–orbit interaction couples the broken parity to the Néel order parameter direction. We demonstrate a novel tool to image the Néel vector direction, N, by combining spatially resolved momentum microscopy with ab-initio calculations that correlate the broken parity with the vector N.

Journal of synchrotron radiation 28(6), 1891 - 1908 (2021). doi:10.1107/S1600577521010511, The small time gaps of synchrotron radiation in conventional multi-bunch mode (100-500 MHz) or laser-based sources with high pulse rate (similar to 80 MHz) are prohibitive for time-of-flight (ToF) based photoelectron spectroscopy. Detectors with time resolution in the 100ps range yield only 20-100 resolved time slices within the small time gap. Here we present two techniques of implementing efficient ToF recording at sources with high repetition rate. A fast electron-optical beam blanking unit with GHz bandwidth, integrated in a photoelectron momentum microscope, allows electron-optical 'pulse-picking' with any desired repetition period. Aberration-free momentum distributions have been recorded at reduced pulse periods of 5 MHz (at MAXII) and 1.25 MHz (at BESSYII). The approach is compared with two alternative solutions: a bandpass pre-filter (here a hemispherical analyzer) or a parasitic four-bunch island-orbit pulse train, coexisting with the multi-bunch pattern on the main orbit. Chopping in the time domain or bandpass pre-selection in the energy domain can both enable efficient ToF spectroscopy and photoelectron momentum microscopy at 100-500 MHz synchrotrons, highly repetitive lasers or cavity-enhanced high-harmonic sources. The high photon flux of a UV-laser (80 MHz, Published by Wiley-Blackwell, [S.l.]

Objectives Several plaque and lesion characteristics have been associated with an increased risk for procedural stroke during or shortly after carotid artery stenting (CAS). While technical advancements in stent design and cerebral protection devices (CPD) may help reduce the procedural stroke risk, and anatomy remains important, tailoring stenting procedures according to plaque and lesion characteristics might be a useful strategy in reducing stroke associated with CAS. In this descriptive report of the ongoing Asymptomatic Carotid Surgery Trial-2 (ACST-2), it was assessed whether choice for stent and use or type of CPD was influenced by plaque and lesion characteristics. Materials and methods Trial patients who underwent CAS between 2008 and 2015 were included in this study. Chi-square statistics were used to study the effects of plaque echolucency, ipsilateral preocclusive disease (90–99%), and contralateral high-grade stenosis (>50%) or occlusion of the carotid artery on interventionalists' choice for stent and CPD. Differences in treatment preference between specialties were also analysed. Results In this study, 831 patients from 88 ACST-2 centres were included. Almost all procedures were performed by either interventional radiologists (50%) or vascular surgeons (45%). Plaque echolucency, ipsilateral preocclusive disease (90–99%), and significant contralateral stenosis (>50%) or occlusion did not affect the choice of stent or either the use of cerebral protection and type of CPD employed (i.e., filter/flow reversal). Vascular surgeons used a CPD significantly more often than interventional radiologists (98.6% vs. 76.3%; p < .001), but this choice did not appear to be dependent on patient characteristics. Conclusions In ACST-2, plaque characteristics and severity of stenosis did not primarily determine interventionalists' choice of stent or use or type of CPD, suggesting that other factors, such as vascular anatomy or personal and centre preference, may be more important. Stent and CPD use was highly heterogeneous among participating European centres.

We report on the structural and magnetic properties of epitaxial thin films of the ferromagnetic shape memory material Ni–Mn–Ga prepared by DC magnetron sputter deposition. Different substrate materials, i.e., MgO(100) and Al2O3(11−20) allow for a tailored epitaxial growth. Using a sacrificial chromium buffer layer freestanding epitaxial films are obtained. In combination with photolithography partially freestanding structures such as microbridges are fabricated. The complex martensite crystal structure in substrate-constrained and freestanding films is studied by means of X-ray diffraction. The identified asymmetric twin variant configuration is associated with a macroscopic surface pattern observed by optical microscopy. The absence of magnetic-field induced strain in the (100) oriented samples is explained on basis of the detected twin variant configuration using a simplified model. Taking advantage of the thin film geometry spectroscopic methods are applied to the samples. The measurements provide the first experimental test for changes in the electronic structure of the involved 3d metals during a martensitic transition. Exploiting the X-ray magnetic circular dichroism quantitative information on the element-specific spin and orbital magnetic moments are accessed. In addition, angular-dependent experiments allow us to trace the microscopic origin of the magnetic anisotropy in Ni2MnGa improving the fundamental understanding of this material.

Klavikulapseudarthrosen nach Frakturen des mittleren Drittels werden haufig durch lokale Schmerzen, eine eingeschrankte Schulterfunktion oder neurovaskulare Symptome manifest. Ziel einer operativen Behandlung ist die Wiederherstellung einer normalen Klavikulaanatomie mit solider knocherner Durchbauung des ehemaligen Frakturspalts. In dieser Studie wurden 24 Patienten mit einer anatomisch prakonturierten Platte nach Meves bei Klavikulapseudarthrose versorgt, bei 11 Patienten wurde eine zusatzliche Spongiosaplastik durchgefuhrt. 19 Patienten konnten nach einem mittleren Zeitraum von 74,5 Monaten nachuntersucht werden. Bei samtlichen Patienten zeigte sich eine knocherne Konsolidierung. Der Constant-Score verbesserte sich von praoperativen 70,4 auf postoperative 82,5 Punkte (89,3% altersadaptiert). 16 Patienten waren sehr zufrieden bzw. zufrieden mit dem operativen Ergebnis. In unseren Handen zeigte sich eine sichere Ausheilung der Klavikulapseudarthrosen unter Verwendung der anatomisch prakonturierten Platte nach Meves bei guten bis sehr guten funktionellen Ergebnissen.

Element-specific magnetic properties of ultrathin epitaxial Co2FeSi(110) films were measured using x-ray magnetic circular dichroism (XMCD). The epitaxial Heusler films were grown by RF magnetron sputtering on substrates. The magnetization of thicker films as determined by XMCD is smaller than expected for a half-metallic material. In addition, the magnetization decreases considerably for films thinner than 10 nm. The thickness dependence of the magnetic moment can be described by introducing a certain number of dead layers representing a deficiency of magnetization at the interfaces. Quantitative evaluation results in a dead layer thickness of 0.8 nm at room temperature, consisting of a temperature induced size effect of 0.1 nm and a surface effect of 0.15 nm at the top and 0.55 nm at the bottom interface.

Co2Mn1−xFexSi Heusler alloys with Fe concentration x = 0–0.4 as prepared by arc melting show a L21 long range order for all Fe concentrations. Magnetic properties of Co2Mn1−xFexSi Heusler alloys were investigated by magnetometry and circular magnetic dichroism. The magnetization of the Fe doped Heusler alloys is in agreement with the Slater–Pauling values expected for half-metallic ferromagnets. Element specific magnetic moments as determined by x-ray absorption using the total electron yield method are in disagreement with theoretical predictions for x = 0 but approach the predicted values as the Fe concentration increases. Surprisingly small Fe concentration increases the magnetic moments of all constituents considerably.

We investigate element-specific spin and orbital magnetic moments of polycrystalline bulk Heusler alloys that are predicted to be half-metallic with composition Co2YZ (Y = Ti, Cr, Mn, Fe and Z = Al, Ga, Si, Ge, Sn, Sb) using magnetic circular dichroism in X-ray absorption spectroscopy (XAS/XMCD). In addition to stoichiometric compounds we also investigate composition series with partly replaced elements on the Y-site (Co2Fe x Cr1−x Si, Co2Mn x Ti1−x Si and Co2Mn x Ti1−x Ge) and on the Z-site (Co2MnGa1−x Ge x ) promising a tailoring of the Fermi level with respect to the minority band gap. We compare experimental results with theoretical predictions elucidating the influence of local disorder in the experimental samples. Moreover, we demonstrate that a consideration of electron correlation in local density approximation theories is necessary for reproducing experimental results. Increased orbital magnetic moments in respect to theoretical predictions put forward the role of spin–orbit coupling for half-metallic properties. For the case of single crystalline thin films we developed a method of simultaneous measurement of bulk and surface sensitive magnetic properties including those at the crucial interface to a tunneling barrier. Exploiting the comparison of bulk and interface information, film growth can be improved for specific applications. In order to directly determine the spin-resolved density-of-states function we present a calculation scheme for extracting this information from the XMCD spectra considering final-state electron correlations. We investigate the electronic properties of epitaxial Co2(Fe x Mn1−x )Si, Co2Fe(Al1−x Si x ), and Co2(Cr0.6Fe0.4)Al films on MgO(100) substrates and for the case of several bulk samples including Co2TiSb as a reference sample for normal metallic ferromagnetism. The experimental results, revealing the distribution of magnetic moments and the relative position of the Fermi energy as a function of the number of valence electrons, confirm the predicted possibility of tailoring the minority band gap using substitutional quaternary Heusler compounds. These findings may be of general importance for the understanding of the electronic structures in complex intermetallic compounds.

The mutual influence of phase transformations, magnetism, and electronic properties of magnetic-shape memory Heusler materials is a basic issue of electronic structure calculations based on density functional theory. In this article, we show that these calculations can be pursued to finite temperatures, which allows to derive on a first-principles basis the temperature versus composition phase diagram of the pseudo-binary Ni-Mn-(Ga, In, Sn, Sb) system. The free energy calculations show that the phonon contribution stabilizes the body-centered-cubic (bcc)-like austenite structure at elevated temperatures, whereas magnetism favors the low-temperature martensite phase with body-centered-tetragonal (bct) or rather face-centered-tetragonal (fct) structure. The calculations also allow to make predictions of magnetostructural and magnetic field induced properties of other (new) magnetic Heusler alloys not based on NiMn such as Co-Ni-(Ga-Zn) and Fe-Co-Ni-(Ga-Zn) intermetallic compounds.

Element-specific magnetic properties of epitaxial Co${}_{2}$Fe${}_{x}$Mn${}_{1\ensuremath{-}x}$Si/MgO(100) Heusler films prepared by laser ablation are measured by circular dichroism in x-ray absorption spectroscopy (XMCD). Surface and bulk magnetization of the 100-nm-thick films are equal as tested by comparing the total electron yield and transmission measurements and follow the generalized Slater-Pauling rule. For Co${}_{2}$FeSi, the large magnetization of 6 ${\ensuremath{\mu}}_{B}$ per formula unit indicates half-metallic behavior. Calculations using the local spin density approximation (LDA) result in a half-metallic band structure for this compound when an additional electron-electron-correlation correction ($\text{LDA}+U$) is considered. Simulated XMCD spectra using the LDA and $\text{LDA}+U$ approaches are compared to the experimental spectra. While the electron-electron Coulomb correlation has only a small effect on the observable XMCD spectra, the calculations predict that it will cause a significant change in the x-ray magnetic linear dichroism (XMLD).

A series of Al and MgO-capped Co${}_{2}$FeAl${}_{0.5}$Si${}_{0.5}$ epitaxial thin films grown on MgO with various levels of L2${}_{1}$ ordering was obtained by in situ annealing. The films were studied by means of x-ray absorption spectroscopy, x-ray magnetic circular dichroism (XMCD), magneto-optical Kerr effect magnetometry, and Brillouin light scattering. We find the anisotropy constants decrease, while the spin wave stiffness increases as the samples are annealed to higher temperatures. The magnetization as determined by Brillouin light scattering reveals a maximum value at intermediate annealing temperatures. Surprisingly, the orbital-to-spin-moment ratio (as seen from XMCD) is essentially stable through the sample series and does not change upon annealing, despite the observed changes in anisotropy and exchange.

We investigate the distribution of element-specific magnetic moments and changes in the spin-resolved unoccupied density of states in a series of half-metallic ${\text{Co}}_{2}({\text{Mn}}_{x}{\text{Ti}}_{1\ensuremath{-}x})\text{Ge}$ Heusler alloys using x-ray magnetic circular dichroism. The Co and Mn magnetic moments are oriented parallel while a small Ti moment shows antiparallel to the mean magnetization. The element-specific magnetic moments remain almost independent on the composition. Therefore, a replacement of Ti by Mn results in an increase in magnetization. The increase in magnetization with increasing $x$ follows the Slater-Pauling rule. The Fermi level decreases with respect to the minority band gap with increasing number of valence electrons. This counterintuitive behavior is explained qualitatively by a charge transfer model and quantitatively by ab initio band-structure calculations.

Strained coherent film growth is commonly either limited to ultrathin films or low strains. Here, we present an approach to achieve high strains in thicker films, by using materials with inherent structural instabilities. As an example, 50 nm thick epitaxial films of the ${\mathrm{Fe}}_{70}{\mathrm{Pd}}_{30}$ magnetic shape memory alloy are examined. Strained coherent growth on various substrates allows us to adjust the tetragonal distortion from $c/{a}_{\mathrm{bct}}=1.09$ to 1.39, covering most of the Bain transformation path from fcc to bcc crystal structure. Magnetometry and x-ray circular dichroism measurements show that the Curie temperature, orbital magnetic moment, and magnetocrystalline anisotropy change over broad ranges.

We investigated element-specific magnetic moments and the spin-resolved unoccupied density of states (DOS) of polycrystalline ${\text{Co}}_{2}\text{Ti}Z$ $(Z=\text{Si},\text{ }\text{Ge},\text{ }\text{Sn},\text{ }\text{Sb})$, ${\text{Co}}_{2}{\text{Mn}}_{x}{\text{Ti}}_{1\ensuremath{-}x}\text{Si}$ and ${\text{Co}}_{2}{\text{MnGa}}_{1\ensuremath{-}x}{\text{Ge}}_{x}$ Heusler alloys using circular dichroism in x-ray absorption spectroscopy (XMCD). We find a small $(l0.03{\ensuremath{\mu}}_{B})$ Ti moment oriented antiparallel and a large $(g3{\ensuremath{\mu}}_{B})$ Mn moment oriented parallel to the Co moment of approximately $1{\ensuremath{\mu}}_{B}$ per atom in the investigated compounds. Orbital magnetic moments are increased for quaternary compounds compared to the corresponding ternary compounds with $x=0$ or $x=1$. The unoccupied spin-resolved partial DOS at the Co atom was extracted from the XMCD data. In the case of ${\text{Co}}_{2}\text{TiSi}$, ${\text{Co}}_{2}\text{TiGe}$, and ${\text{Co}}_{2}\text{TiSn}$, the Co minority DOS reveals a maximum at 0.5 eV above ${E}_{F}$ and very low values at ${E}_{F}$ in agreement with the expectation for half-metallic ferromagnetism. In contrast, ${\text{Co}}_{2}\text{TiSb}$ shows a large minority DOS at the Fermi energy like a normal metal. A substitution of Ti by Mn in ${\text{Co}}_{2}\text{TiSi}$ shifts the minority DOS maximum from 0.5 to 0.9 eV with respect to the Fermi energy. For the series ${\text{Co}}_{2}{\text{MnGa}}_{1\ensuremath{-}x}{\text{Ge}}_{x}$ we observe a gradual shift of the minority DOS maximum from 0.7 eV for $x=1$ to 1.0 eV for $x=0$, indicating half-metallic ferromagnetism for the whole series. Our results, revealing the distribution of magnetic moments and the relative position of the Fermi energy as a function of the number of valence electrons, confirm the predicted possibility of tailoring the minority band gap using substitutional quaternary Heusler compounds. The results maybe of general importance for the understanding of the electronic structures in complex intermetallic compounds.

We investigate the electronic properties of epitaxial ${\text{Co}}_{2}({\text{Fe}}_{x}{\text{Mn}}_{1\ensuremath{-}x})\text{Si}$, ${\text{Co}}_{2}\text{Fe}({\text{Al}}_{1\ensuremath{-}x}{\text{Si}}_{x})$, and ${\text{Co}}_{2}({\text{Cr}}_{0.6}{\text{Fe}}_{0.4})\text{Al}$ films on MgO(100) substrates using circular dichroism in x-ray absorption spectroscopy (XMCD). Considering final-state electron correlations, the spin-resolved partial density of states at the Co atom can be extracted from XMCD data. The experimental results corroborate the predicted half-metallic ferromagnetic properties of these alloys and reveal a compositional dependence of the Fermi energy position within the minority band gap.

We have investigated the magnetic properties of epitaxial Heusler alloy films using x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism∈dex{x-ray!magnetic circular dichroism} (XMCD) in the transmission (TM) and in the surface sensitive total electron yield (TEY) mode. We have investigated Ni_2MnGa based shape memory alloys and half-metallic Co2Cro.6Feo.4 films. Single crystalline Ni2MnGa(110)/Al2O3(1120) and Ni2MnGa(100)/MgO(100) films show a martensitic transition from a cubic high temperature phase to a martensitic low-temperature phase at 250–275 K as concluded from magnetometry and x-ray diffraction. The martensitic transition of this Heusler compound is shifted in films on Al2O3 to higher temperatures Tm=276 K compared to the bulk value of 200 K. A remarkable change of the Ni x-ray absorption spectra occurs at Tm indicating specific changes of the electronic structure. The observed changes are in agreement with theoretical predictions. The orbital to spin momentum ratio of the Ni moment increases significantly on entering the martensite state thus explaining the macroscopic increase of magnetic anisotropy. The spin and orbital magnetic moments of Co2Cro.6Feo.4 films are similar to values measured for the bulk materials of the corresponding compounds. Interface properties can severely deviate from the bulk properties. We have investigated the interfaces of Co2Cro.6Feo.4 and Ni2MnGa Heusler alloy films and Al cap layers. At elevated temperatures and at rough surfaces the deposited Al severely reacts with the surface of a Heusler alloy indicated by changes of the absorption spectra. Compositional deviations at the interface as detected by XAS can also severely influence magnetic interface properties. Micro-spectroscopy using photoemission electron microscopy reveals an Al surface reaction proceeding inhomogeneously with reaction nuclei separated on a micron length scale.

Pseudarthroses of the clavicle after fractures of the medial third often present with local pain, compromised shoulder function, or neurovascular symptoms. Reconstruction of normal clavicular anatomy and solid fusion is a prerequisite for good clinical outcome after surgical treatment. In this study, 24 patients with clavicular pseudarthrosis were treated with the anatomical precontoured Meves plate. In 11 patients, additional bone grafting was done.Nineteen patients could be reexamined with a mean follow-up of 74.5 months. In all of them, solid fusion was achieved.The Constant score improved from 70.4 points preoperatively up to 82.5 points postoperatively (89.3% age-related). Sixteen patients were satisfied or very satisfied with the operative result.In our patients, secure healing of clavicular nonunion was achieved with the anatomical precontoured Meves plate, with good or excellent clinical outcomes.

We investigate the martensitic transition of single crystalline Ni2MnGa 110 /Al2O3 1120 and Ni2MnGa 100 /MgO 100 films using magnetometry, x-ray diffraction, x-ray absorption spectroscopy, and x-ray magnetic circular dichroism. The martensitic transition from the cubic austenite phase to the low symmetry martensite phase depends strongly on the chosen substrate. For 110 oriented films on Al2O3, the martensitic phase is significantly more stable than for the 100 oriented films on MgO. A remarkable change of the Ni x-ray absorption spectra occurs at the transition, indicating specific changes of the electronic structure. The observed changes are in agreement with theoretical predictions. The orbital to spin momentum ratio of the Ni moment increases significantly on entering the martensite state, thus explaining the macroscopic increase of magnetic anisotropy.

We have grown thin films of the Heusler compound ${\mathrm{Co}}_{2}\mathrm{Fe}\mathrm{Si}$ by RF magnetron sputtering. On (100)-oriented MgO substrates we find fully epitaxial (100)-oriented and $L{2}_{1}$ ordered growth. On ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}(11\overline{2}0)$ substrates, the film growth is (110)-oriented, and several in-plane epitaxial domains are observed. The temperature dependence of the electrical resistivity shows a power law with an exponent of $7∕2$ at low temperatures. Investigation of the bulk magnetic properties reveals an extrapolated saturation magnetization of $5.0{\ensuremath{\mu}}_{B}∕\mathrm{f.u.}$ at $0\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The films on ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ show an in-plane uniaxial anisotropy, while the epitaxial films are magnetically isotropic in the plane. Measurements of the x-ray magnetic circular dichroism of the films allowed us to determine element specific magnetic moments. Finally we have measured the spin polarization at the surface region by spin-resolved near-threshold photoemission and found it strongly reduced in contrast to the expected bulk value of 100%. Possible reasons for the reduced magnetization are discussed.

We investigate different types of disorder which are predicted to influence the spin polarization by x-ray and electron diffraction (RHEED). We observe that the compound Co2FeAl grows in the B2 ordered structure. However, for Co2FeAl0.3Si0.7 the analysis revealed with increasing annealing temperature a crossover from B2 to L21 order. The magnetization of the samples is investigated by SQUID magnetometry and x-ray magnetic circular dichroism (XMCD) experiments in bulk sensitive transmission and surface sensitive total electron yield (TEY) mode. The results reveal the same surface and bulk moments of Co2FeAl. However, with increasing annealing temperature the Co2FeAl0.3Si0.7 thin films display a small decrease of the surface moment in contrast to a not changing bulk moment. This observation is relevant concerning potential device applications of Co2FeAl0.3Si0.7.

The interface and bulk magnetic properties of epitaxial thin films of the Heusler compounds Co2Cr0.6Fe0.4Al/Mg/AlOx and CoCr2Al/Mg/AlOx are investigated. We compare the magnetization measured by x-ray magnetic circular dichroism experiments in surface sensitive total electron yield mode (information depth of 2–3 nm) and in bulk sensitive transmission mode. The pronounced temperature dependence of the magnetoresistance of tunneling junctions with Heusler electrodes, which is often related to weakened interface magnetism, is discussed. Evidence is given that this explanation does not apply to the compounds investigated here.

The influence of 30 keV He$^+$ ion irradiation on structural, electronic and magnetic properties of Co$_2$MnSi thin films with B2 order was investigated. It was found, that irradiation with light ions can improve the local chemical order. This provokes changes of the electronic structure and element-specific magnetization towards the bulk properties of the well-ordered Co$_2$MnSi Heusler compound with L2$_1$ structure., Comment: 4 pages, 4 figures

Element-specific magnetic moments were investigated for epitaxial Ni2Mn1+xGa1−x and (Ni2MnGa)1−x(Co2FeSi)x Heusler films using x-ray absorption spectroscopy and x-ray circular magnetic dichroism in transmission. The epitaxial films of the Ni2MnGa-derived compositions were prepared by dc-sputtering on Al2O3 substrates at 773 K. X-ray diffraction confirms a (1 1 0) oriented growth. An increase in the Mn concentration reduces the magnetic spin moment of both Mn and Ni. An increase in the content of Co2FeSi in the Ni2MnGa compound leads to an increase in the Mn and Ni spin moments and to a decrease in Tm for 5% Co2FeSi and finally to a suppression of the phase transition for 20% Co2FeSi. The orbital moments of the stoichiometric Ni2MnGa films are larger compared with values obtained for films of a Mn-rich compound and smaller compared with Co2FeSi containing films. The results are discussed in the context of theoretical models.

X-ray magnetic circular dichroism (XMCD) of core-level absorption (x-ray absorption spectroscopy, XAS) spectra in the soft x-ray region has been measured for the ferromagnetic Heusler alloy Rh2MnGe at the Rh M3,2 and Mn L3,2 edges. The ratio of Rh and Mn spin moments amounts to 0.05 which is smaller than the ratio of 0.1 determined by a local density approximation electronic band structure calculation. We have found that the orbital moments of the Rh 4d and Mn 3d states are very small. The observed Rh 2p XAS spectrum can be understood on the basis of the Rh 3d partial density of unoccupied states as is typical for metals. The observed features of the Mn 2p XAS and XMCD spectra are dominated by final state multiplets as is typical for oxides. The comparison of experimental and ab initio calculated XAS/XMCD spectra reveals a strong narrowing of the Mn 3d bands, indicating strongly localized Mn moments. The magnetic moments are considerably more localized for Rh2MnGe in comparison with the isoelectronic compound Co2MnGe. In spite of the strong localization of the Mn moment, the temperature dependences of sublattice magnetization are equal for the Mn and Rh sublattices in contrast to the prediction by a Heisenberg model. This might be attributed to the remaining itinerant character of the Rh moment.

We investigated magnetic and structural properties at the surface of epitaxial Ni2MnGa(110) Heusler films using x-ray absorption spectroscopy and x-ray magnetic circular dichroism both in transmission and total electron yield mode. The magnetic shape memory films were prepared by dc sputtering from a stoichiometric target onto sapphire substrates at an optimized substrate temperature of 773K. X-ray diffraction confirms a (110) oriented growth on Al2O3(112¯0) and an austenite to martensite transition at 270–280K. At the surface the martensitic phase transition and the magnetization are strongly suppressed. The deviation in the surface properties is caused by a Mn deficiency near the surface.

Threshold photoemission excited by polarization-modulated ultraviolet femtosecond laser light is exploited for phase-sensitive detection of magnetic circular dichroism (MCD) for a magnetite thin film. Magnetite (Fe(3)O(4)) shows a magnetic circular dichroism of ∼(4.5 ± 0.3) × 10(-3) for perpendicularly incident circularly polarized light and a magnetization vector switched parallel and antiparallel to the helicity vector by an external magnetic field. The asymmetry in threshold photoemission is discussed in comparison to the magneto-optical Kerr effect. The optical MCD contrast in threshold photoemission will provide a basis for future laboratory photoemission studies on magnetic surfaces.

In this report, we provide an x-ray magnetic circular dichroism (XMCD) study for 100nm thick epitaxial magnetite (Fe3O4) films on MgO (001) and Al2O3 (0001) substrates. For XMCD, we recorded the surface sensitive total electron yield and the bulk sensitive transmission spectra. From the analysis of the XMCD data, we find an increased Fe spin moment (10% larger) at the surface of the film on MgO (100) with respect to the corresponding bulk value of the film. Surface and bulk spin moments of the film on Al2O3(0001) are almost equal. For both films, the bulk orbital to spin moments ratio increases from zero at 70K to 0.03–0.04 at 300K. For Fe3O4∕MgO (001), the surface orbital to spin moment ratio behaves similarly to the bulk value, while the orbital to spin moments ratio is increased at the Fe3O4∕Al2O3 (0001) surface to 0.06. The observed differences between films grown on MgO and Al2O3 are explained within the framework of differences in mismatch strain experienced by the films.

We have investigated the solid state reaction at the interface of Co2Cr0.6Fe0.4Al, Co2FeSi, and Ni2MnGa Heusler alloy films and Al cap layers using x-ray absorption spectroscopy in transmission and total electron yield mode. At elevated temperatures and at rough surfaces the deposited Al severely reacts with the surface of a Heusler alloy indicated by changes of the absorption spectra. Microspectroscopy using photoemission electron microscopy reveals that the reaction proceeds inhomogeneously with reaction nuclei separated on a micron length scale.

The bias voltage and magnetization direction dependent differential conductivity dI∕dV(Vbias) of tunneling junctions with the Heusler compound Co2Cr0.6Fe0.4Al (CCFA) was investigated. The junctions contain AlOx tunneling barriers and Co counter electrodes. A pronounced shoulder in the differential conductivity with parallel electrode magnetization and a sign change of the tunneling magnetoresistance at a bias voltage of ≃±500 mV were the most prominent features observed. The measurements are discussed in the framework of band structure related effects and inelastic excitations. X-ray absorption spectroscopy (XAS-TEY) investigations show that the CCFA/Al interface has an increased Fe content compared to the sputter target composition, presumably due to Fe buffer layer interdiffusion.

Element specific magnetization has been determined at the surface and in the bulk of Co2Cr0.6Fe0.4Al Heusler alloy films grown on alpha-Al2O3 and capped by Al, using x-ray magnetic circular dichroism both in transmission and total electron yield. The magnetic moments for Co and Fe are considerably reduced at the upper surface in comparison to their values in the bulk of the film. The large reduction at room temperature of 17% for thick films averaged along the electron escape depth implies an even larger reduction at the topmost layer which is crucial for spin-dependent transport. The surface magnetization decreases additionally with respect to the bulk value with decreasing film thickness below 20 nm.

The properties of iron nanostructures prepared by shallow incidence molecular beam epitaxy on faceted α-Al2O3 (101¯0) (m plane) are described. Depending on the angle of deposition with regard to the sapphire surface, the morphology of the structures reaches from pearl-necklet-like strung nanodrops to laced nanowires. Crystallographic measurements reveal at least four epitaxial close to (211)-oriented twins. Magnetization measurements performed at room temperature in a vibrating sample magnetometer and magneto-optical Kerr rotation measurements reveal an easy axis of magnetization close to the facet ridges. Still, the shape of the hysteresis loops depends strongly on the morphology of the samples. The magnetization reversal process can be described by the formation of a magnetic vortex structure.

A magnetically induced shape memory effect in Ni2MnGa results in huge magnetostrictive effects of several percent. Using x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD) we investigated element specific magnetic moments and electronic structure of single crystalline, (110) oriented Ni2MnGa films on a-plane Al2O3 substrates in the austenite and martensite state. The structural phase transition of the samples is evident from temperature dependent x-ray diffraction and magnetization measurements. The Ni XAS differ significantly for temperatures above and below the martensite transition in agreement with published ab-initio calculations. Using XAS in transmission geometry on our thin film samples we observe the corresponding reduction of the absorption feature as predicted by theoretical calculations. The XMCD analysis shows the orbital contribution of the Ni electrons to be responsible for the magnetic anisotropy.