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840 items found (0 items not approved), displaying 791 to 800.[First/Prev] 76, 77, 78, 79, 80, 81, 82, 83 [Next/Last]

Instruments / Technical Area	Publication Details	Published
Theoretical Physics	Electronic and magnetic structure of GaxFe1−x thin films E. Arenholz , A. Mcclure , Y. Idzerda , G. Van Der Laan Physical Review B 82 (18), 180405 DOI: 10.1103/PhysRevB.82.180405 Show Abstract ▼ Abstract: The electronic as well as magnetic properties of GaxFe1−x films were studied by soft x-ray measurements. Using x-ray magnetic circular dichroism the Fe majority-spin band was found to be completely filled for x≈0.3. With further enhanced Ga content, the Fe moment as well as the angular dependence of the x-ray magnetic linear dichroism decrease strongly, which we attribute to the formation of D03 precipitates. Moreover, the magnetocrystalline anisotropy drops significantly.	Nov 2010
I16-Materials and Magnetism	Ferromagnetism at the interfaces of antiferromagnetic FeRh epilayers R. Fan , C. J. Kinane , T. R. Charlton , R. Dorner , M. Ali , M. A. De Vries , R. M. D. Brydson , C. H. Marrows , B. J. Hickey , D. A. Arena , B. K. Tanner , G. Nisbet , S. Langridge Physical Review B 82, 184418 DOI: 10.1103/PhysRevB.82.184418 Show Abstract ▼ Abstract: The nanoscale magnetic structure of FeRh epilayers has been studied by polarized neutron reflectometry. Epitaxial films with a nominal thickness of 500 Å were grown on MgO (001) substrates via molecular-beam epitaxy and capped with 20 Å of MgO. The FeRh films show a clear transition from the antiferromagnetic (AF) state to the ferromagnetic (FM) state with increasing temperature. Surprisingly the films possess a FM moment even at a temperature 80 K below the AF-FM transition temperature of the film. We have quantified the magnitude and spatial extent of this FM moment, which is confined to within ∼ 60 – 80 Å of the FeRh near the top and bottom interfaces. These interfacial FM layers account for the unusual effects previously observed in films with thickness < 100 Å . Given the delicate energy balance between the AF and FM ground states we suggest a metastable FM state resides near to the interface within an AF matrix. The length scale over which the FM region resides is consistent with the strained regions of the film.	Nov 2010
Theoretical Physics	Compositional and structural medium energy ion scattering study of the temperature mediated diffusion determination at the Co/V interface in Co/V/MgO(100) M. Diaz , L. Martinez , E. Roman , A. Redondo-Cubero , M. Muñoz-Márquez , G. Van Der Laan , N. D. Telling , P. Bailey , T. C. Q. Noakes , Y. Huttel Surface Science DOI: 10.1016/j.susc.2010.09.011 Show Abstract ▼ Abstract: The impact of annealing at 300 °C on the elemental composition and the atomic structure of the Co/V interface in the 2.5 Å Co/70 Å V/MgO (100) system has been investigated by medium energy ion scattering (MEIS) using 100 keV He+ ions. By combining the experimental MEIS results with simulations we show that, while the Co/V interface is abrupt for the system kept at room temperature, annealing at 300 °C induces a strong interdiffusion leading to a Co0.5V0.5 surface bcc alloy with a high degree of disorder. Additionally, the MEIS data suggest that the surface of the annealed system is slightly rumpled by ~ 0.2 Å.	Oct 2010
	Tilting during island growth of In2O3 on Y-stabilized ZrO2(001) revealed by high-resolution x-ray diffraction R. A. Cowley , A. Bourlange , J. L. Hutchison , K. H. L. Zhang , A. Korsunsky , R. G. Egdell Physical Review B 82 (16) DOI: 10.1103/PhysRevB.82.165312 Show Abstract ▼ Abstract: The growth of In2O3 islands on (001)-oriented Y-stabilized cubic ZrO2 has been investigated using high-resolution x-ray diffraction and the results compared with those from atomic force microscopy and electron microscopy. Measurements were performed with wave-vector transfer both parallel to and perpendicular to the surface normal. Transverse scans around the epilayer (004) and (008) reflections gave a characteristic three-peak structure for wave-vector transfer along the [110] direction but a two-peak structure when the scan was performed along the [100] direction. These results suggest that the atomic planes of the islands are not parallel to those of the substrate but are tilted at an angle of about 0.7° from the four different in-plane ⟨110⟩ directions. Tilting was also observed in real space by high-resolution transmission electron microscopy. The tilt helps to relieve tensile strain arising from a −1.6% lattice mismatch between the epilayer and the substrate. The tilt direction is shown to be determined by the elastic constants of the epilayer, which favor strain along ⟨110⟩ directions rather than ⟨100⟩ directions. The x-ray results also indicated that the islands imaged by atomic force microscopy are each built up from microdomains so that the coherence length deduced from x-ray scattering is much smaller than the island size. Thus for islands with a thickness of 2500 Å the coherence length was estimated to be about 500 Å.	Oct 2010
I06-Nanoscience	Origin of magnetism in cobalt-doped indium tin oxide thin films A. M. H. R. Hakimi , F. Schoofs , R. Bali , N. A. Stelmashenko , M. G. Blamire , S. Langridge , S. A. Cavill , G. Van Der Laan , S. S. Dhesi Physical Review B 82 (14), 144429 DOI: 10.1103/PhysRevB.82.144429 Show Abstract ▼ Abstract: We report an x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) study of a 5.4 at. % Co-doped indium tin oxide (ITO) thin film shown to exhibit ferromagnetism beyond room temperature. The XAS spectra at the Co L2,3 edge reveal pronounced multiplet features characteristic of divalent octahedrally coordinated Co2+ ions. The results suggest that the Co2+ ions are nonmetallic and substitute for the In site in ITO. Magnetic field and temperature-dependent XMCD spectra imply that the Co2+ ions give a paramagnetic contribution to the overall ferromagnetic response both at the near-surface region and throughout the bulk of the films. No magnetic polarization was detected at the In M2,3 or Sn M2,3 edges. We therefore presume that the ferromagnetism observed is a result of the sp-d exchange interaction between the sp band of the host ITO and that of the localized d electrons of the transition-metal Co dopants.	Oct 2010
	Probing ferroelectricity in PbZr0.2Ti0.8O3 with polarized soft x rays E. Arenholz , G. Van Der Laan , A. Fraile-Rodríguez , P. Yu , Q. He , R. Ramesh Physical Review B 82 (14) DOI: 10.1103/PhysRevB.82.140103 Show Abstract ▼ Abstract: The reduction in symmetry associated with the onset of ferroelectric order in PbZr 0.2 Ti 0.8 O 3 (PZT) thin films leads to a pronounced difference at the Ti L 3 , 2 absorption edges between spectra measured with the x-ray linear polarization perpendicular and parallel to the ferroelectric polarization. We introduce a general method to analyze the observed difference spectra using atomic multiplet calculations. Moreover, we find experimental evidence for structural changes in PZT induced by the reversal of the ferroelectric polarization.	Oct 2010
I07-Surface & interface diffraction	Assembly of poly(methacrylate)/purple membrane lamellar nanocomposite films by intercalation and in situ polymerisation Andrew M. Collins , Noor Haida Mohd Kaus , Francesca Speranza , Wuge H. Briscoe , Daniel Rhinow , Norbert Hamp , Stephen Mann Journal Of Materials Chemistry DOI: 10.1039/C0JM01358G Show Abstract ▼ Abstract: Thin films comprising ordered stacks of purple membrane (PM) sheets containing the light-driven proton pump bacteriorhodopsin (BR) were infiltrated with methacrylic acid (MA) monomers to produce lamellar bionanocomposites. Subsequent in situ polymerization and crosslinking of the guest MA molecules resulted in partially intercalated poly(methacrylate)/PM freestanding films, which showed increased stability in water, structural integrity and enhanced resistance to ethanol degradation compared with PM control films or non-polymerized MA/PM layered nanocomposites. Studies on photocycle kinetics confirmed that the polymerized PM films were functionally active, and showed an increase in the lifetime for the M-state intermediate of the photocycle. The results indicate that nanometre-thin layers of crosslinked poly(methacrylate) can be synthesized in situ between the PM sheets to produce novel functional bionanocomposites with proton transfer and photochromic properties.	Sep 2010
I06-Nanoscience	Strain dependent defect mediated ferromagnetism in Mn-doped and undoped ZnO thin films Frank Schoofs , Thomas Fix , Ali M. R. H. Hakimi , Sarnjeet S. Dhesi , Gerrit Van Der Laan , Stuart A. Cavill , Sean Langridge , Judith L. Macmanus-Driscoll , Mark G. Blamire Journal Of Applied Physics 108 (5), 053911 DOI: 10.1063/1.3455856 Show Abstract ▼ Abstract: The structural and magnetic properties of pulsed laser deposited zinc oxide thin films have been investigated. Room temperature ferromagnetism is present in undoped as well as Mn-doped films. The saturation magnetization of the thin films reveals a dependence on both the composition and the out of plane lattice parameter. X-ray magnetic circular dichroism down to 2 K reveals a purely paramagnetic contribution from the Mn in Mn:ZnO films. We conclude that the observed ferromagnetism arises entirely from intrinsic defects in the ZnO which can be varied by manipulation of the lattice parameter.	Sep 2010
Theoretical Physics	Strain-induced changes in the electronic structure of MnCr2O4 thin films probed by X-ray magnetic circular dichroism G. Van Der Laan , R. V. Chopdekar , Y. Suzuki , E. Arenholz Physical Review Letters 105 (6), 067405 DOI: 10.1103/PhysRevLett.105.067405 PMID: 20868013 Show Abstract ▼ Abstract: We show that the angular dependence of x-ray magnetic circular dichroism (XMCD) is strongly sensitive to strain-induced electronic structure changes in magnetic transition metal oxides. We observe a pronounced dependence of the XMCD spectral shape on the experimental geometry as well as nonvanishing XMCD with distinct spectral features in transverse geometry in compressively strained MnCr2O4 films. The angular dependent XMCD can be described as a sum over an isotropic and anisotropic contribution, the latter linearly proportional to the axial distortion due to strain. The XMCD spectra are well reproduced by atomic multiplet calculations.	Aug 2010
	Step interactions on Pt(111) vicinal surfaces determined by grazing incidence X-ray diffraction: Influence of the step orientation G. Prevot , L. Barbier , P. Steadman Surface Science 604 (15-16), 1265-1272 DOI: 10.1016/j.susc.2010.04.012 Show Abstract ▼ Abstract: We have studied the step step interactions on the Pt(997) vicinal surface. Grazing incidence X-ray diffraction (GIXD) allowed us to measure the elastic atomic relaxations near the surface due to the steps. By means of the model of buried elastic dipoles, within the framework of anisotropic linear elasticity (ALE) calculations, the surface stress of Pt(111), and the elastic interaction between steps are deduced. The values so-obtained are compared to the values previously measured on the Pt(779) surface with the same technique. The comparison shows the strong influence of step geometry on step interactions.	Aug 2010

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