bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetism and Magnetic Interactions at Transition Metal Surfaces and Interfaces
Authors: Wu Ruqian , Wang Dingsheng , Freeman A.J. 
Published: September 2012

ABSTRACTIn the exciting field of low dimensional magnetic systems including surfaces, interfaces and thin-films, local spin density (LSD) functional ab initio electronic structure calculations have played a key role by not only providing a clearer understanding of the experimental observations but also predicting new systems with desired properties. Our extensive calculated results demonstrate that: (i) Magnetic clean surfaces or interfaces with inert substrates undergo strong magnetic moment enhancements; (ii) the strong interaction with nonmagnetic transition metals diminishes (completely in some cases) the ferromagnetism and usually stabilizes the antiferromag-netic configuration. By including spin-orbit coupling as a perturbation, (i) reliable results for the Magneto-crystalline anisotropy of ultra-thin films can be obtained using the state-tracking procedure, although the anisotropy energy is a few tenths of a MeV; (ii) spectra of the Magneto-optical Kerr effects and magnetic circular dichroism in the soft x-ray region can be determined.
Mechanism for the magnetoresistance of Pure Bulk Ferromagnets and Composite Thin Film Structures
Authors: Stearns Mary Beth 
Published: September 2012

ABSTRACTA unified explanation is given of the long-standing question of the origin of the low-field magnetoresistance, MR, behavior in pure ferromagnetics and the large magnetoresistance effects seen in magnetic layered and granular structures. It is shown that the main contributions to these effects are due to the scattering that occurs at the magnetic boundaries between non-aligned magnetic regions. This scattering occurs because the predominant conduction electrons in 3d ferromagnetics are the highly polarized itinerant d electrons. As a result of this polarization the Majority-band d electrons are strongly reflected at an antiparallel magnetic boundary due to a lack of available states for occupancy. The traversing electrons are further scattered as they cross the boundary due to a discontinuity in the potential caused by the interchange of their kinetic and exchange energies at the boundary. Expressions for the magnetoresistance due to these scattering mechanisms are derived and shown to describe very well the wide variety of magnetoresistance values and other features found in the literature for both pure Fe and nano-structures of Fe or Co with non-Magnetic Materials. The MR Magnitude is seen to vary inversely with the domain size. Thus the domain size and sample purity are seen to be the main factors that determine the magnitude of the MR effect in pure ferromagnets. The large MR values seen in layered and granular magnetic structures arise from the small effective domain size attainable in these structures. This is achieved by introducing a non-Magnetic Material into these structures which allows the effective domain size to be decreased from the micron range of the pure ferromagnetic elements into the nanometer range.
Probing the Surface-Vacuum Interface with Spin-Sensitive Metastable Atom Deexcitation, Electron Capture and Electron Emission Spectroscopies
Authors: Walters G. K. , Rau C. 
Published: September 2012

ABSTRACTSpin-Polarized Metastable Atom Deexcitation (SPMDS) and Electron Capture (ECS) Spectroscopies probe the exponential tails of electronic wavefunctions extending from the surface into the vacuum, and are consequently extremely sensitive to the surface-vacuum interface. The use of SPMDS to probe the near-surface vacuum magnetization of Ni (l 10) and Fe (l 10) and the dramatic changes that result upon exposure to ambient gases is discussed, as is the use of ECS and Spin-Polarized Electron EMission Spectroscopy (SPEES) to determine the ferromagnetic and critical behavior of surfaces and ultra-thin epitaxial systems.
Spin Polarized Photoemission Studies of Quantum well States in Thin Films
Authors: Johnson P.D. , Brookes N.B. , Chang Y. , Garrison K. 
Published: September 2012

ABSTRACTSpin polarized photoemission is used to study the electronic structure of noble metals deposited on ferromagnetic substrates. Studies of Ag deposited on an Fe (001) substrate reveal a series of minority spin interface or quantum well states with binding energies dependent on the thickness of the silver. Similar behavior is observed for Cu films deposited on a fee Co (001) substrate. Tight-binding Modeling reproduces many of the observations and shows that hybridization of the sp-bands with the noble metal d-bands cannot be ignored.
Magnetic Spectro-Microscopy Using Magneto-Dichroic Effects in Photon-Induced Auger Electron Emission
Authors: Schneider C.M. , Meinel K. , Holldack K. , Oepen H.P. , Grunze M. , Kirschner J. 
Published: September 2012

ABSTRACTWe have imaged the magnetic domain structure on the surface of Fe (100) single crystals using energy resolved photoemission microscopy with circularly polarized soft x-rays. The contrast between different domains arises due to Magneto-dichroic effects in the emitted Auger electrons. This new approach offers a surface sensitive way to combine chemical and magnetic information on a microscopic scale.
MCD Observed by Photoemission on the 2p Lines of Iron Films Under an External Applied Field.
Authors: Boeglin C. , Beaurepaire E. , Carrière B. , Hricovini K. , Krill G. 
Published: September 2012

ABSTRACTCircular Dichroic X-ray Photoemission Spectroscopy (CDXPS) experiments have been performed on the 2p core level spectra of polycrystalline Fe film which was magnetized by a low excitation field. The ability to perform the CDXPS experiments in a non remanent mode at a photon energy of 2100 eV opens new and interesting possibilities for the MCD technique in the study of surface and interface Magnetism. Our work on this polycrystalline iron gives some new insights into the understanding of the MCD Mechanism. First results show a similar angular variation for the measured asymmetry, as those observed on a Fe bcc (100) single crystal remanently magnetized in the [100] direction. Our results make clear that the parameters governing the behaviour of the asymmetry factor (A) are not completely described by the relative direction of the Magnetization (M) with the polarization vector of the incident beam (q) and the direction of detection of the photoelectrons (z). The specific outcoming of this work is to clearly show that this behaviour of A is not connected to the crystalline structure of the film for our geometries.
Strong Magnetic Circular Dichroism in 4F Photoemission
Authors: Starke Kai , Navas E. , Baumgarten L. , Kaindl G. 
Published: September 2012

ABSTRACTWe report on strong magnetic circular dichroism (MCD) in 4f photoemission (PE) from Magnetized Gd(0001)/W(110) films. The shape of the 4f6–7FJ final-state PE Multiplet depends on the relative orientation between photon spin and sample magnetization and can be described within an atomic Model. The spectra rule out antiferromagnetic alignment of the (0001) surface layer and the bulk of Gd. This MCD in 4f-PE from rare-earth materials opens new perspectives in the analysis of surface and thin-film magnetism and as a sensor for circular polarization of soft x-rays.
Auger Electron and Photoelectron Diffraction in Magnetic Thin Films
Authors: Idzerda Y.U. , Ramaker D.E. 
Published: September 2012

ABSTRACTThe role of the final-state character of the emitted electron in Auger electron diffraction (AED) and x-ray photoelectron diffraction (XPD) is examined with respect to magnetic materials. Single scattering cluster calculations with the inclusion of the spherical wave character and the final-state character of the emitted electron (both angular momentum quantum number and magnetic quantum number) show that selective emission from different M-levels, generated by a non-statistical distribution of initial M-levels or by an M-selective excitation process, results in distinctly different emission patterns.
Perpendicular Magnetic Anisotropy in Ultrathin Fe (110) Films on Cr (110)
Authors: Fritzscht Helmut , Gradmann Ulrich 
Published: September 2012

ABSTRACTIn contrast to Fe(110) -films on W(110), which are magnetized always in the plane as a result of easy-plane magnetic surface anisotropies (MSA), Fe(110) -films on Cr(110) show perpendicular magnetization up to a thickness of roughly 3 Monolayers, as a result of a perpendicular MSA of the Fe(110)/Cr/(110) interface. Acoordingly, Fe(110) -films on W(110), covered with Cr(110), show asymmetric MSA, the easy-plane mSA of the W(110)/Fe(110) -interface opposing the perpendicular one of the Fe(110)/Cr(110) -interface. It turns out that MSA is asymmetric too in Fe(110) films on W(110) covered by Cu, Ag, Au or UHV.
Microstructural Dependence of the Perpendicular Magnetic Anisotropy in Co-Pt Alloys
Authors: Marinero E. E. , Farrow R. F. C. , Harp G. R. , Geiss R. H. , Bain J. A. , Clemens B. 
Published: September 2012

ABSTRACTTo establish the structural origins of the perpendicular magnetic anisotropy in Co-Pt alloys, a variety of magnetic and structural characterization techniques have been utilized. We have determined that the development of out-of-plane magnetization in these alloys, strongly depends on growth temperature and in contrast to CO/Pt Multilayers, the highest anisotropics and coercivities are observed in polycrystalline alloys with negligible preferred crystallographic orientation. Lattice strain Measurements, surface roughness determination and crystal growth studies indicate that contributions from magnetostrictive and magnetostatic contributions to the perpendicular anisotropy in these alloys are not significant. H RTEM and synchrotron-based x-ray diffraction experiments, on the other hand, confirm the existence of ordered CoPt3 at elevated temperatures. We suggest that the strong temperature dependence of the perpendicular anisotropy is correlated to the onset of spontaneous chemical ordering during the growth which results in anisotropie pair ordering. A tentative model explaining this strong temperature dependence is described.
UHV Preparation and In-Situ Surface Analysis of MNFE/Nife Exchange Structures: Interfacial Impurity Incorporation
Authors: Cohen Susan L. , Baker John M. , Russak Michael A. , Scilla Gerald J. , Hwang Cherngye , Rossnagel Stephen M. 
Published: September 2012

ABSTRACTMnFe/NiFe exchange structures have been prepared in an ultra-high vacuum sputtering/surface analysis system. Controlled introduction of residual gas impurities such as O2 and H2O at the MnFe/NiFe interface is studied by in-situ x-ray photoelectron spectroscopy (XPS) and the exchange structures are magnetically characterized. Due to the extreme reactivity of the NiFe surface towards O2, the exchange coupling is severely degraded by only small exposures of this molecule to the NiFe surface. In contrast, H2O does not oxidize the NiFe surface and therefore can be tolerated in greater quantities in the sputtering chamber without detrimental loss of exchange. This understanding of the basic surface chemistry of the MnFe and NiFe surfaces can lead to improved sputtering practices in actual manufacturing applications.
Application of High-Resolution Electron Microscopy to the Study of Magnetic Thin Films and Multilayers
Authors: Sinclair R. , Nolan T.P. , Bertero G.A. , Visokay M.R. 
Published: September 2012

ABSTRACTThe performance of a wide range of modern magnetic thin-film materials for information storage is found to depend dramatically on grain nucleation and coherence at interfaces. Three such systems, Fe/Pt Multilayers, CO/Pt Multilayers, and CoCrTa/Cr bilayers are considered here. High-resolution electron Microscopy (HREM) shows that ordered CoPt and FePt L1o structures can be formed and oriented, using coherence with the substrate, with their magnetically easy c-axes perpendicular to the film plane. This orientation results in the perpendicular magnetization required for Magneto-optic recording Media. Different sputtering gases used in producing CO/Pt Multilayers result in varying degrees of interfacial intermixing, which is shown to strongly affect the perpendicular magnetic anisotropy energy. The required high in-plane coercivity of longitudinal recording media is also correlated with the observed interface coherence and the resulting oriented growth of CoCrTa with the magnetically hard <110> axis perpendicular to the film plane. Many features of the microstructure can be observed directly at the atomic level by HREM, and so the usefulness of this technique is emphasized in this paper.
Initial Growth and morphology of Ultrathin Magnetic Films Studied Using Scanning Tunneling Microscopy.
Authors: Chambliss David D. , Johnson K.E. , Kalki K. , Chiang S. , Wilson R.J. 
Published: September 2012

ABSTRACTThe room-temperature growth of Fe on Cu(100) has been studied using the scanning tunneling Microscope (STM) to determine low-coverage growth mode and local structures related to the FCC-BCC structural transformation. Results for submonolayer deposition demonstrate an initial interchange of deposited Fe atoms with substrate Cu. This leads to a highly rough Fe-Cu interface and growth characteristics that for different experimental techniques can resemble 3-D island growth or layer-by-layer growth. For a thickness ∼14 Monolayers, the FCC-BCC transition is observed to occur via the formation of fairly large martensitic grains, rather than by a change in atomic aggregation. The implications of the instability of FCC-Fe, as evident in both low- and high-coverage data, are considered.
Scanning-Ion Microscopy with Polarization Analysis (Simpa)
Authors: Zheng N. J. , Rau C. 
Published: September 2012

ABSTRACTWe have developed a novel, high-resolution magnetic imaging technique, scanning-ion microscopy with polarization analysis (SIMPA). In SIMPA, a highly-focused, scanning Ga+ ion beam is used to excite spin-polarized electrons at surfaces of ferromagnetic Materials. By Measuring the intensity and the spin polarization of the emitted electrons using a newly developed, compact mott polarimeter, topographic and magnetic images of magnetic structures are obtained. We report on first SIMPA studies on single-crystalline Fe samples.
Structure and Magnetic Properties of FE/ZR Multilayer Films
Authors: Konno Toyohiko J. , Nakayama Takenori , Clemens Bruce M. , Sinclair Robert 
Published: September 2012

ABSTRACTWe investigated structural and magnetic properties of Fe/Zr Multilayer films using high-resolution transmission electron Microscopy, X-ray diffraction and vibrating sample Magnetometry. For films with wavelength (Λ) ≥ 80Å, the interface region between the Fe and Zr layers exhibits a 15–20Å thick amorphous structure. The Magnetization curves of these films showed a monotonous decrease in the saturation magnetizations with Λ, whose trend is well explained by a simple asymptotic model that assumes the interface amorphous layer to be non-ferromagnetic. Films with Λ≤40Å exhibit a compositionally-Modulated amorphous structure. The latter films are paramagnetic except for the one with Λ=40Å, which showed a superparamagnetic behavior.
Structural and Magnetoresistance Properties of Co/Cu Multilayers Doped with Fe
Authors: George J.M. , Barthelemy A. , Durand O. , Duvail J. L. , Fert A. , Galtffir P. , Heckmann O. , Pereira L.G. , Petroff F. , Valet T. 
Published: September 2012

ABSTRACTWe have studied the influence of ultra-thin interfacial Fe layers on the structural and magnetoresistance properties of CO/Cu Multilayers. Our results show that the giant magnetoresistance arises from spin dependent scattering at the CO/Cu interfaces and in the bulk of Co, the interfacial contribution being predominant. We also demonstrate that the close-packed crystallographic structure of Co and Cu is very sensitive to the insertion of interfacial bec Fe layers: for small thicknesses, Co as well as Cu adopt a metastable bec structure.
Resistance and magnetoresistance of Gadolinium/Tungsten Multilayers
Authors: Heys A. , Donovan P. E. , Astrakharchik E. G. , George B. 
Published: September 2012

ABSTRACTThe resistance and magnetoresistance of Gd/W Multilayers have been measured at temperatures between 300K and 4K and in fields of up to 7 Tesla. The temperature coefficent of resistance is strongly influenced by the thickness of the Gd layers, becoming negative at a Gd layer thickness of 0.8nm. The Magnetoresistance is dominated by the Gd below about 100K. Multilayers which show reduced saturation magnetisation at 4K also have an unusual form of magnetoresistance around 100K. We suggest that this may be due to antiferromagnetic alignment of the Gd and W Moments at low applied fields.
Transmission Electron Microscopy Studies of NiFe/Cu/Co/Cu on Si.
Authors: Gautier P. , Valet T. , Durand O. , Jacquet J.C. , Chevalier J.P. 
Published: September 2012

ABSTRACT(NiFe/Cu/Co/Cu) Multilayers grown on (100) Si by RF sputtering have been studied by transmission electron Microscopy. The samples are found to be polycristalline and are only weakly textured. The period of the multilayers is clearly visible by small angle electron diffraction and Fresnel imaging. The waviness of the layers appears to be related to the columnar structure of the samples. Experimental images with Fresnel contrast are compared with simulations in order to assess the thickness and roughness of each individual layer.
Neutron Scattering Measurements of the Staggered Magnetization of an Antiferromagnetic Epitaxial thin Film FeF2
Authors: Belanger D. P. , Lui M. , Erwin R. W. 
Published: September 2012

ABSTRACTElastic neutron scattering measurements performed at the NIST reactor have been used to measure the staggered magnetization near the transition temperature in a thin antiferromagnetic epitaxial film of FeF2 of thickness 0.8μm and diameter 1cm grown on a diamagnetic (001) ZnF2substrate by MBE. The use of a thin film permits extinction-free Bragg intensities, something which has proven impossible in bulk crystals. The growth techniques yield sufficient crystal quality to observed resolution limited Magnetic Bragg scattering peaks and to approach the transition within a reduced temperature of |t| = 0.003. The structure quality of this sample has been characterized using X-ray double crystal diffraction with a measured rocking curve lin ewidth of less than 30 arc sec. The sample thickness, while small enough to eliminate extinction, is sufficiently large to assure three-dimensional Ising Model critical behavior. We indeed observe critical behavior consistent with theoretical predictions. The success of the thin film experiments demonstrates the possibilities of extinction-free Bragg scattering measurements in a variety of antiferromagnetic Materials, including multilayered systems.
A Comparative Study of Structural, Magnetic, and Transport Properties of Co-Re Superlattices Sputtered on Glass and Si Substrates
Authors: Leal J.L. , Barradas N.P. , Soares J.C. , da Silva M.F. , Rots M. , Freitas P.P. 
Published: September 2012

ABSTRACTAntiferromagnetically coupled (Co17A°Re5A°)×15 superlattices were deposited simultaneously onto glass and Si substrates, with an intervening Re buffer layer. Samples grown on glass show sharper interfaces than those grown on Si. This effect reflects on Magnetoresistance, Magnetization, Rutherford backscattering, and hyperfine field results. The influence of the Re buffer layer thickness and annealing temperature on these properties is discussed.
Interfacial Exchange Coupling and the magnetization of Iron Oxide/Nickel Oxide Superlattices
Authors: Berry S. D. , Lind D. M. , Lochner E. , Shaw K. A. , Hilton D. , Erwin R. W. , Borchers J. A. 
Published: September 2012

ABSTRACTThe role of interfacial exchange coupling in the magnetic behavior of metal oxide materials has been investigated through the study of Fe3O4/NiO superlattices. We report results on a series of superlattices grown where one bilayer constituent was held to a fixed thickness while varying the other from single unit cell dimensions upward. High crystalline quality was confirmed by XRD, RHEED and neutron diffraction. Magnetization profiles show substantial deviations from bulklike iron oxide results, with an increase in domain rotation energies observed in the superlattices over that of bulk iron oxide (increasing with NiO layer thickness) indicating the strong nature of Fe3O4/NiO interfacial linkage. Neutron scattering at elevated temperatures shows that the NiO remains ordered above the 523 K bulk Néel temperature. This suggests that at least a portion of the NiO within a layer remains ordered well above the Néel temperature, with an increase in effective Néel transition temperature that approaches the Fe3O4 Curie temperature in the limit of very thin NiO layers. Although the exchange coupling dominates these effects, strain also plays an important role.
Interface and Volume Anisotropy of MBE-Grown Co/Pt (111), (110) and (001) and Sputtered CO/Pt Multilayers
Authors: Weiler D. , Farrow R.F.C. , Marks R.F. , Harp G.R. , Notarys H. , Gorman G. 
Published: September 2012

ABSTRACTA quantitative determination of interface (Ks) and volume anisotropy {?ψ) constants of MBE and sputtered CO/Pt Multilayers is reported. Torque and VSM Magnetometry were used to determine the total average anisotropy and the room temperature magnetization of four different series of films with varying Co thickness and nearly constant Pt thickness. All films were characterized with X-ray diffraction and X-ray fluorescence, allowing the determination of the “Magnetic” volume with good accuracy. Both Ks and Jeff are found to be orientation dependent. We find the following results for MBE films grown on Ag buffered GaAs substrates and highly < 111 > textured films, grown on etched SiNx buffers:(111) Ks = 0.97mJ/m2, Kveff =-0.74MJ/m3 MBE(111) Ks = 0.92mJ/m2, Kveff =-l.lIMJ/m3 sputtered(110) Ks = 0.42mJ/m2, Kveff =-l.95MJ/m3 MBE(001) Ks = 0.59mJ/m2, Kveff =-5.98MJ/m3 MBEThe [110]-oriented MBE films show in addition a large (intrinsic) in-plane anisotropy constant K‖0≃-3MJ/m3 which is found to be independent of the Co thickness. [100] is the easy and [110] the hard in-plane direction.
Valence Instability and Magnetic Polarization of Ce Atoms near the Interface of Ce/Fe Multilayers Studied by Magnetic Circular X-Ray Dichroism.
Authors: Klose F. , Pizzini S. , Giorgetti C. , Schulte O. , Baudelet F. , Dartyge E. , Krill G. , Felsch W. , Fontaine A. 
Published: September 2012

ABSTRACTAn experimental study of conventional x-ray absorption and of magnetic circular x-ray dichroism has been performed on Ce/Fe Multilayers at the Ce L2,3 and the Fe-K edge, to characterize the impact of the interaction of Ce and Fe on the local electronic and magnetic structure of the interface. The spectra reveal that the interaction has two effects. First, on a depth scale of up to 15 A near the interface, the Ce atoms adopt the electronic structure of the oc-phase, with itinerant 4f states. Second, a large portion (=10 Å) of these cc-like Ce atoms is magnetically polarized and carries an ordered Magnetic 5d Moment. The Fe-3d and Ce-5d Moments are antiferromagnetically coupled. Interface Mixing on a length scale of the magnetic polarization can be excluded.